Boulton Paul Overstrand gun turret

Boulton Paul Overstrand gun turret



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Boulton Paul Overstrand gun turret


The Boulton Paul Overstrand was the first aircraft to be equipped with a fully-enclosed power-operated gun turret. It was also the last biplane bomber to enter RAF service, and remained in front line service until 1938.


Gun Turret - Aircraft

At first, guns on aircraft were either fixed in orientation or mounted on pedestals or simple swivel mounts. The latter evolved into the Scarff ring, a rotating ring mount which allowed the gun to be turned to any direction with the gunner remaining directly behind it. As aircraft flew higher and faster, the need for protection from the elements led to the enclosure or shielding of the gun positions, as in the "lobsterback" rear seat of the Hawker Demon fighter.

The first bomber in the Royal Air Force to carry an enclosed power operated turret was the Boulton Paul Overstrand which first flew in 1933. The Overstrand had a single turret, which was at the front of the bomber fitted with one machine gun. Movement of the gun on its mount actuated motors that rotated the turret.

The American Martin B-10 all-metal monocoque monoplane bomber introduced turret-mounted defensive armament within the United States Army Air Corps, almost simultaneously with the RAF's Overstrand biplane bomber design. The Martin XB-10 prototype aircraft first featured the nose turret in June 1932, and was first produced as the YB-10 service test version by November 1933. The production B-10B version started service with the USAAC in July 1935.

In time the number of turrets carried and the number of guns mounted increased. RAF heavy bombers of World War II typically had three powered turrets, with the rear one—the tail gunner or "Tail End Charlie" position—mounting the heaviest armament of four 0.303 inch Browning machine guns or, late in the war, two AN/M2 light-barrel versions of the American Browning M2 machine gun.

During the World War II era, British turrets were largely self-contained units, manufactured by Boulton Paul Aircraft and Nash & Thomson. The same model of turret might be fitted to several different aircraft types. Some models included gun-laying radar that could lead the target and compensate for bullet drop.

The UK introduced the concept of the "turret fighter", with aeroplanes such as the Boulton Paul Defiant where the armament (4 x 0.303 in (7.7 mm) machineguns) was in a turret mounted behind the pilot rather than in fixed positions in the wings. The concept came at a time when the standard armament of a fighter was only two machine guns. In the face of heavily armed bombers operating in formation it was felt that a group of turret fighters would be able to concentrate their fire flexibly on the bombers making beam, astern and from below attacks practicable.

Although the idea had some merits in attacking bombers, it was found to be impractical when dealing with other fighters the weight and drag of the turret impaired the airplane's speed and maneuverability relative to a conventional fighter which the flexibility of the turret armament could not compensate for. At the same time conventional fighter designs were flying with 8 or more machine guns. Attempts to put heavier armament (multiple 20 mm cannon) in low profile aerodynamic turrets were explored by the British but not successful.

Not all turret designs put the gunner in the turret along with the armament. Both the Americans and Germans produced aircraft with remote controlled turrets. In the US, the large, purpose-built Northrop P-61 Black Widow night fighter was produced with a remotely-operated dorsal turret that had a wide range of fire though in practice it was generally fired directly forward under control of the pilot. For the last production blocks of the B-17F, and for all versions of the B-17G Flying Fortress a twin-gun remotely operated "chin" turret, designed by Bendix and first used on the experimental YB-40 "gunship" version of the Fortress, was added to give more forward defence. Specifically designed to be compact and not obstruct the bombardier, it was operated by a hand-controller and aimed by a reflector sight mounted in the windscreen.

The intended replacement for the German Bf 110 heavy fighter, the Messerschmitt Me 210, possessed twin half-teardrop-shaped, remotely-operated Ferngerichtete Drehringseitenlafette FDSL 131/1B turrets, one on each side "flank" of the rear fuselage to defend the rear of the aircraft, controlled from the rear area of the cockpit. By 1942, the German He 177A Greif heavy bomber would feature a Fernbedienbare Drehlafette FDL 131Z remotely operated forward dorsal turret, armed with twin 13mm MG 131 machine guns on the top of the fuselage, which was operated from a rotating "astrodome" just behind the cockpit glazing — a second, manned dorsal turret, further aft on the fuselage was also used on most examples. The US B-29 Superfortress had four remote controlled turrets operated from the pressurised sections in the nose and middle of the aircraft with one gunner directing the others.

The defensive turret on bombers fell from favour with the realization that bombers could not attempt heavily defended targets without escort regardless of their defensive armament unless very high loss rates were acceptable, and the performance penalty from the weight and drag of turrets reduced speed, range and payload and increased the number of crew required. The British de Havilland Mosquito light bomber was designed without any defensive armament and used its speed to avoid engagement with fighters.

A small number of aircraft continued to use turrets however—in particular maritime patrol aircraft such as the Avro Shackleton used one as an offensive weapon against small unarmoured surface targets. The Boeing B-52 jet bomber and many of its contemporaries (particularly Russian) featured a tail-mounted barbette (a term from British English), or "remote turret" —an unmanned turret but often with more limited field of fire.


Why Britain’s World War II Turret Fighters Failed

Squadron Leader Philip Hunter (in the aircraft marked PS-A) leads a quartet of Boulton Paul Defiant Mk.I fighters of No. 264 Squadron during the summer of 1940.

Arming a fighter plane with nothing more than a four-gun turret proved unique—but not brilliantly successful.

The German pilot could scarcely believe his luck as he approached a British fighter west of Dunkirk on May 27, 1940. The Englander, apparently a Hawker Hurricane, was taking no evasive action as the Messerschmitt Me-109E fighter closed in from behind.

Suddenly and unexpectedly, four .303-caliber Browning machine guns blazed from a turret in the British fighter’s fuselage. Mortally hit, the 109 fell victim to Squadron Leader Philip A. Hunter of No. 264 Squadron, Royal Air Force (RAF), and his gunner, Sergeant F.H. King—and to an unusual addition to the RAF arsenal, the Boulton Paul Defiant.

Over the next few days, more Messerschmitts would suffer a similar fate before they got the measure of the new British fighter—but when they did, the encounters would have a very different outcome.

The story of the Defiant actually began during the previous war, when the British were enjoying great success with a two-seat fighter, the Bristol F.2B. What seems to have been forgotten by the RAF soon after World War I, however, was that the Bristols gained a formidable reputation by being flown like single-seaters, using the front gun as their principal offensive weapon and the gunner only for rear defense.

The RAF replaced its aging Bristols in 1931 with the Hawker Demon, a fighter version of Hawker’s versatile Hart two-seat day bomber, along with a shipboard variant, the Osprey. The rear gunner’s cockpit on the Demon was equipped with the same .303-caliber Lewis machine gun and manually operated Scarff mounting ring used on World War I aircraft with half the Demon’s 200-mph speed. The gunners had difficulty clearing jams and changing ammunition drums with freezing fingers, plus the force of the slipstream made among the gun difficult.

A later version of the Demon was fitted with a Frazier-Nash gun mount with power-assisted traverse and a windscreen for the gunner. Thus equipped, the Demon’s gunnery scores went up dramatically, but the gunner was still exposed to the elements, and his gun still had to be manually elevated and aimed. In addition, the single Lewis gun was proving inadequate against a new generation of faster and more heavily armed fighters.

One aviation firm closely concerned with the problem was Boulton Paul Aircraft Ltd., the company that had been subcontracted by Hawker to build most of the Demons for the RAF. Originally a woodworking concern based in Norwich, England, Boulton and Paul Ltd. (as it was originally called) built Camel fighters during World War I under license from Sopwith, the predecessor of Hawker. In addition to the Demon, Boulton Paul in the 1930s was producing twin-engined bomber for the RAF called the Sidestrand, and its gunners were experiencing difficulties similar to those reported by gunners of the two-seaters.

Boulton Paul developed its own pneumatically powered gun turret in 1933 for an improved version of the Sidestrand bomber called the Overstrand. Boulton Paul staff members were then approached by the French company Society d’Applications des Machines Motrices (SAMM), which offered production rights to a gun turret designed by one of its engineers, J.B.A. de Boysson.


No. 264 Squadron was the first to be equipped with the Defiant, taking it into combat through the early days of the Battle of Britain. It became a night fighter unit after disastrous losses during daylight operations and converted to de Havilland Mosquito Mk. IIs in May 1942. (IWM CH873)

The French Armee de l’Air had shown no interest in the idea of a power-operated gun turret. SAMM therefore was eager to recoup some of the development cost of the project by selling it to the British. A fully enclosed, electrohydraulically operated unit capable of incorporating either four machine guns or a 20mm cannon, the French turret was capable of a 360-degree traverse and elevation up to 85-degrees above the horizon by means of a single control stick.

Boulton Paul installed a four-gun de Boysson turret in the nose of an Overstrand bomber to demonstrate it to the Air Ministry. The next logical step was to develop a two-seat fighter equipped with the turret. The now aging Hawker Demon was too small and underpowered to accommodate the heavy turret, so an entirely new aircraft had to be designed. The Air Ministry issued a specification in April 1935 outlining the design parameters for the new plane. The primary mission of the plane was to attack incoming bomber formations with its four-gun turret, either from below or from the side. It was also originally to have been equipped with light bomb racks for a secondary ground attack role, but that requirement was later dropped. Since the turret fighter was expected to attack in conjunction with the new Hawker Hurricane, its performance was expected approximate that of a conventional single-seat fighter.

Royal Air Force pilots felt that the turret fighter would stand little chance against a modern, single-seat fighter, but it was never intended to encounter such opposition. The nearest prospective enemy bombers were expected to have to fly all the way from Germany, far beyond the range of escorting fighters.

At that stage, the Air Ministry issued the fateful decree that the new fighter’s armament should be restricted solely to the turret’s .303 Browning machine guns. Part of the reason was a desire to save weight. There was also a prevailing belief that the turret constituted the aircraft’s principal armament, and the pilot should be compelled to regard it as such. It was feared that, should the pilot be provided with forward firing armament, he would be tempted to use the aircraft in a conventional manner, and thus cancel out the turret’s supposed advantage. Essentially, the pilot became a chauffeur for his gunner—a role that probably did not go down well with aggressive fighter pilots.


A gunner of No. 264 Squadron prepares to enter the turret of his Defiant. He is wearing a GQ Parasuit, supplied exclusively to Defiant gunners, which incorporated a parachute harness and life-saving jacket. (IWM CH874)

Boulton Paul’s new fighter, called the Defiant, superficially resembled the Hurricane and Spitfire. But it was in no sense a copy of either. Designed by J.D. North, the Defiant was an all-metal, low-wing monoplane with a monocoque fuselage and retractable landing gear. It was powered by the same 1,030-hp Rolls-Royce Merlin III liquid-cooled engine used by its single-seat stablemates. The radiator was mounted under the center section of the wing, as on the Hurricane.

The Defiant achieved a reasonably high speed despite its bulky turret because of the careful attention Boulton Paul had paid to streamlining. Retractable fairings, hydraulically operated, were installed behind and in front of the turret to smooth the airflow over the fuselage when the turret was not in use.

The Defiant pilot’s cockpit was provided with a sliding canopy, but the gunner entered his turret through an automobile-type door in the fuselage side. The RAF considered that a potentially hazardous arrangement, so the turret was redesigned with an access hatch in the roof, plus an emergency escape hatch in the floor. The electrically fired turret guns were provided with an interrupter mechanism to prevent the gunner from accidentally shooting his own aircraft. Likewise, to keep the radio antenna out of the line of fire, the Defiant’s designers had to install it below the fuselage. They devised a method of automatically retracting that vulnerable equipment into the plane’s belly whenever the landing gear was lowered.

The Defiant was quite compact for a two-seat fighter—only 3 1/2 feet longer than the Hurricane and with nearly a foot less wingspan. It weighed 6,078 pounds empty and had a gross weight of 8,600 pounds, compared with the Hurricane’s empty and gross weights of 4,743 and 6,218 pounds, respectively. That extra weight resulted in a top speed of 302 mph at 16,500 feet, compared to 316 mph for the Hurricane. It also took the Defiant 11.4 minutes to reach that altitude, compared to only 6 1/2 minutes for the Hurricane.

The Defiant prototype was first flown on August 11, 1937, but the first squadron to be equipped with the new fighters, No. 264, was not deployed until December 1939. The reasoner the delay was that the Defiant was developed during a period when Boulton Paul was in the process of a corporate reorganization and was also relocating from Norwich to a new plant in Wolverhampton.

Despite the Defiant’s protracted development, that of its main rival, the Hawker Hotspur, had been even slower, due to Hawker’s preoccupation with production of its new Hurricane. Production of the Hotspur would have depended on Boulton Paul in any case, since the latter owned the sole British merchandising rights to the four-gun power turret.

The Defiant’s first saw action with No. 264 Squadron against the Luftwaffe on May 12, 1940, downing two Junkers Ju-88As. The next day, however, the Defiant’s ran into their first Bf-109Es, and though they downed five, they lost an equal number of their own planes.

In subsequent fighting over Dunkirk in late May, the Defiant’s initially presented a shock to German fighter pilots who, thinking they were attacking a Hurricane from the rear, suddenly found themselves on the wrong end of a quartet of Brownings. During that period, Defiants piloted by Squadron Leader P.A. Hunter and Nicholas G. Cooke were credited in downing nine enemy aircraft each. Frederick Desmond Hughes and Eric Gordon Barwell (a pilot and gunner team) accounted for seven. Once Luftwaffe fighter pilots became familiar with the Defiants, they quickly mastered them, and No. 264 Squadron lost 14 aircraft during the last three weeks of May.

The second Defiant squadron, No. 141, fared even worse. In the squadron’s first engagement on June 28, nine of its Defiants tangled with a group of Bf-109Es and lost seven of their number in exchange for only four Messerschmitts. On July 19, nine more Defiants of No. 141 encountered Bf-109Es of Jagdgeschwader 51, and seven more were lost, only one of the enemy being claimed in return by one of the two surviving teams, Flt. Lt. Hugh N. Tamblyn and Sergeant S.W.H. Powell. In order to mitigate further losses, the two Defiant squadrons were pulled back to a sector farther north in England.

With the onset of the Battle of Britain in August 1940, the RAF found itself in desperate need of every fighter it could muster, and the Defiant squadrons found themselves heavily engaged once more. A third unit of Defiants, manned by expatriate Poles, No. 307 Squadron, was organized in September 1940 but did not become operational until September.

After the Battle of Britain reached its climax in September, the Luftwaffe was forced to switch to night-bombing attacks. During. that period, the Defiants were redeployed exclusively as night fighters. By May 1941, RAF Fighter Command had seven operational squadrons of Defiants, and in spite of an initial lack of on-board radar, they were the most successful night fighters in British service during 1941.


The Defiant Mk.II, equipped with A.I. Mark.VI radar and a more powerful Merlin XX engine, performed admirably as a night fighter. (IWM ATP9780B)

An improved version, with built-in radar, was developed specifically for the nocturnal role late in 1940. Designated the Defiant Mark II, it had a 1,260-hp Merlin XX engine that delivered 22 percent more power than the old Merlin III and increased its speed to 315 mph. Because the Defiant II gunner was restricted to the cramped confines of his turret, it was the pilot who was forced to divide his attention between the radar and his normal flight instruments.

Higher-performance night fighters, such as the Bristol Beaufighter and the de Havilland Mosquito, became available, and the Defiant was gradually phased out of front-line service. The last ones were replaced in July 1942. A total of 1,060 Defiants were produced, including 140 of a final version, the Defiant III, built specifically as a target tug.

Boulton Paul did not immediately give up on fighter resign, despite the poor showing of the Defiant. During the desperate summer of 1940, the company submitted a proposal for a single-seat version of the Defiant Mk.II that would be armed with either 12 .303-caliber machine guns or four machine guns and four 20mm cannons in the wings. The company also designed an improved Defiant radar-equipped night fighter called the P-96, which was to be armed with either six wing-mounted cannons or a four-gun turret. The P-96 was to be powered by a 2,200-hp Napier Sabre or a 2,500-hp Bristol Centaurus engine, and was expected to attain a speed of 410 mph. Neither of those proposed aircraft was built.

A carrier-based version of the Defiant had originally been planned as a replacement for the Hawker Osprey. However, the Royal Navy later decided that it would be easier to graft Boulton Paul’s turret onto the net Blackburn Skua fighter/dive bomber. Because of Blackburn’s preoccupation with the production of Skuas for the Navy and Botha torpedo planes for the RAF Coastal Command, all 136 production Rocs, as the turret fighters were called, were built under subcontract by Boulton Paul.


The Defiant's heavy turret met with little success when it was fitted to the already-underpowered Blackburn Roc. (Fleet Air Arm Museum)

First flown on December 23, 1936, the Roc weighed 4 percent more than the Defiant, while its 890-hp Bristol Perseus radial engine delivered 13.5 percent less than the Merlin III. The turret installation was not as aerodynamically clean as the Defiant’s because the Roc had not been designed as a turret fighter. With a top speed of under 225 mph, the ROC was deemed incapable of intercepting anything faster than a flying boat.

A few Rocs were briefly deployed with land-based fighter squadrons alongside the more conventional Skuas, but no squadron was ever equipped entirely with Rocs nor were they ever deployed overseas or aboard carriers. The majority of Rocs ended their days as air-sea-rescue patrol planes or target tugs. The most action they saw was at Gosport. There, four grounded Rocs were dispersed around the naval air station with their turrets permanently manned as anti-aircraft batteries.

Hindsight is always 20-20, and the fallacy of the concept of fighters picking off enemy bombers with broadsides from their multigun turrets now seems obvious. It should be remembered, however, that when the Defiant was designed, those bombers were known to be armed with only three puny 7.7mm machine guns. It never occurred to the RAF planners who conceived the Defiant that France and the Low Countries would capitulate in a matter of weeks, enabling the German Luftwaffe to deploy single-seat escort fighters of the caliber of the Me-109E within range of Britain.

Boulton Paul’s powered turrets proved to be far more successful when installed as defensive armament in bombers than they had been when used offensively in fighters. They were more widely used during the war in such famous aircraft as the Lockheed Hudson, Handley Page Halifax and Avro Lancaster.

This feature originally appeared in the September 1996 issue of Aviation History. To subscribe, click here!

Is it time to add a Defiant replica to your Battle of Britain collection? Click here.


Variants [ edit | edit source ]

Defiant N1671, RAF Museum, 2008

The single surviving complete example of the type is a Defiant I, N1671, on display as a night fighter at the Royal Air Force Museum in Hendon, London. Δ] ⎪] It was one of four Defiants delivered to No. 307 Polish Night Fighter Squadron at RAF Kirton in Lindsey, Lincolnshire, England on 17 September 1940. ⎫] It was passed to No. 153 Squadron at the end of October 41 and 285 Sqn in 1942. In 1954 it was identified for storage as a historical aircraft and passed to the RAF Museum in 1971. The aircraft was moved on 20 May 2009 to Rochester Airport, where it was restored by the Medway Aircraft Preservation Society (MAPS). ⎬] It was returned to Hendon on 6 December 2012. ⎭]

Major parts of at least two other Defiants survive N1766 and N3378, both Mk Is. ⎫]


Boulton Paul Heritage Project

It is with great regret we announce the passing of Jack Holmes on the 27 th September 2020 aged 93.

Jack Holmes

Jack was one of the mainstays of the Boulton Paul Association, and for most of its existence at the old Boulton Paul Aircraft site he was the Chief Engineer of the Association, responsible for the manufacture of the Defiant static replica now at the Battle of Britain Museum, Hawkinge and the Overstrand Nose and Turret replica at Flixton Museum. When the museum had to close he continued to impart his metalworking skills and engineering knowledge to schoolchildren in Wolverhampton.

Jack was a Norwich lad who moved with his family to the general area of Claregate and Bilbrook in 1936 where his father was a key engineering shops manager for Boulton Paul Aircraft, and had been for the previous Boulton & Paul Aircraft and Experimental Department of Norwich. He was taken on in the Print Room during 1941 until a place could be organised in the works drawing office. At the time the company were delivering Defiant Mk.I and II Night Fighters and TT Mk.I Target Tugs plus developing experimental turret designs. It was in 1943 that he met his wife to be, Florence. He was given an apprenticeship dated 2 nd August 1943 which was formally sealed on 16 th August 1944 and accepted by the Board on 24 th August 1944.

As the war moved onwards, despite being indentured to Boulton Paul as an apprentice, Jack felt a need to serve in the services and joined the RAF in 1945, much to the annoyance of the company. He served with 691 sqn at RAF Chivenor in Devon, operating as a winchman on Miles Martinette target tugs. When he returned he had to re-enter the Training School at an apprentice salary to complete his time. V. J. Johnson did not apply any sanctions for breaking his indentures because he and Jack’s father had been old friends. The last part of his apprenticeship was in the flight shed and this turned his head away from the drawing office into a love of hands-on aircraft fitting. His apprenticeship was closed short on 3 rd January 1946, covering 29 months rather than the contracted five years, including his period in the RAF, and noted his completing service in the machine shop and on fuselage, ribs and wing manufacture.

By 1947 he was in the experimental department making parts for the Jet Delta prototypes. He was later tasked to work on the Balliol prototypes and with on-site repairs to the tailwheel mounting of one of the experimental Balliol aircraft, which had taken a hard landing at RAE. By 1950’s he was in charge of the fitting team which had to introduce the first dog-tooth leading edge on to a set of Supermarine Swift Wings. He was also involved in building the first of the Canberra B.I.8, 20mm cannon gun packs and tasked with learning as much as possible of the Redux process, a new method of bonding metal panels together.

He applied to take over a new department within the company in 1953, a dedicated X-Ray facility for inspecting components and looking for internal defects. It was as an apprentice myself in around 1970 that I first met Jack when he had small groups into the department and explained the X-Ray method for the inspection of undercarriage legs and Concorde pipework assemblies for defects.

Jack left the company in 1984 when the decision was made to close the Department and move the X-Ray work to Dowty Cheltenham, leaving Jack and his staff redundant. A small job in a leather shop in Wolverhampton sustained his family until he retired aged 72. He joined the BP Association (then called the BP Society) in 1991, as it was formed, voting for an improvement of its rules and regulations as the BP Association and supporting that Association and its aims for the rest of his life.

His knowledge, friendship, and wit will be sorely missed.

Cyril and Jack receiving The Queens Award for Voluntary Service on behalf of the Association from Lord Lieutenant of Staffordshire, Ian Dudson in 2012.

Les Whitehouse – Association Archivist

12th July 2016

It is with great regret that we have to report the tragic loss of member Vaughn Meers on the 12th July 2016 to a blood clot on the brain. Aged 65, one was constantly reminded of a whirling dervish with all the things he managed to fit into his non-stop life. Vaughn’s enthusiasm for all things wheeled, flying or military in arms, was matched only by his enormous circle of contacts and his copious collection of relics.


A penchant for organisation by any means, beg, borrow or cajole, he was a considerable assist to the Boulton Paul Heritage Centre during their many open days. Those same organisational skills he utilised in his own ‘Wings & Wheels’ events for charity, particularly in the support of the Tettenhall Heritage Centre – with whom he was heavily involved. Vaughn was solidly set in his opinions, which remained virtually unchangeable once decided, with a never give up attitude and, in his own words, “a hide like a rhinoceros”. This bounce back undefeated mind-set made him both friends and foes over the years but he was guaranteed to stand firm on his thoughts. Whichever camp, you may have been in, his presence will be sorely missed by all who knew him his passing undeniably much too soon.

His funeral will be held at Streetly Crematorium on Friday 29th July 2016, at 10:30 am.

Les Whitehouse – Association Archivist

Blue Plaque Unveiled for John Dudley North CBE

W/C 27th July 2015

On the 25th July 2015, members of the Boulton Paul Association joined with the Bridgnorth Civic Society, the Bridgnorth Mayor and Mayoress and specially invited guests to attend the unveiling of a Blue Plaque on the former Bridgnorth home of aviation pioneer John Dudley North CBE, former Managing Director and Chief Engineer of Boulton Paul Aircraft Ltd.

The plaque installed at Eversley House

John Dudley North was born in January 1893 and educated at Bedford School, following the death of his father, he was unable to attend University and instead took up an apprenticeship within marine engineering. His obvious interest in aeronautics and man’s desire to fly led to him transferring to an aeronautical apprenticeship at Hendon under Horatio Barber, he then headed to the factory of Claude Graham White. He rose rapidly to become Chief Designer and Chief Engineer. Following time at Austin, he moved to Boulton & Paul at Norwich to set up the Aeronautical Department. He then formed a consortium to buy the division when it was sold in 1934.

In 1936 the renamed Boulton Paul Aircraft Ltd moved to Pendeford, Wolverhampton and North took up residence at Eversley House, Bridgnorth. He lived there until his death in January 1968, remaining a crucial and integral part of BPA and the aviation industry thoughout this time.

Boulton Paul Association members with the Mayor at the unveiling.

The Mayor spoke of North’s work as a lifetime advocate of improved air safety and his dedication to improvements in aircraft design before unveiling the plaque and then posed for photographs with the Boulton Paul Association members (Left to Right in the image above), Jack Holmes (Chief Engineer), Les Whitehouse (Archivist), Joyce Dunworth (widow of former BPA test pilot, Geoff Dunworth) and Cyril Plimmer (Chairman). An archive display of North’s life (collated by Association Archivist Les Whitehouse) was presented alongside light refreshments from the current owners of Eversley, Mr and Mrs John Murphy.

The Association would like to thank the Bridgnorth Civic Society, the Mayor of Bridgnorth Cllr David Cooper and Mr and Mrs John Murphy for their efforts to get North’s contribution to aviation recognised and the unveiling and refreshments on the day.

Les Whitehouse – Association Archivist

Breaking News

Boulton Paul News Update by Archivist Les Whitehouse
W/C 19th January 2015

The Boulton Paul Defiant has been in the news more than normal in the last three years with the refurbishment of serial N1671 in 307 squadron guise as EW-D by the Medway Aircraft Preservation Society on behalf of the RAF Museum. Then more recently the problems of finding a home for the Boulton Paul Association’s own replica, currently stored by the RAF Museum on behalf of the Association. Classed as a full size model (FSM), this replica is wood clad with Alloy and fabric skinning.

Finished as L7005, 264 squadron PS-B, this replica represents the aircraft last flown by Flt Sgt E. R. “Ted” Thorne and Sgt F. J. “Fred” Barker on 26th August over Herne Bay. Following the combat with Dornier Do17Z bombers and their escorting Bf109 fighters, L7005 was crash landed and wrecked, while one of the bombers attacked by the squadron went on to ditch on the Goodwin Sands, subsequently being the subject of a the recent raising for preservation by the RAF Museum.

The Association is pleased to announce this week that it has completed the deal to preserve the replica L7005 by donating it to the Battle of Britain Museum at Hawkinge in Kent. It only remains to arrange a specific date for the replica to be moved from RAFM Cosford deep store to its new home.

Also this week saw the transport of other Boulton Paul Association’s artifacts into permanent preservation. The Boulton & Paul P.6 replica Boulton & Paul P.75 Overstrand replica nose Gnat ground trainer nose and the nose of a two seat Hunter (finished as the sole Hunter Mk 12, the “Green Hunter” used for extensive Boulton Paul Aircraft “fly-by-wire” flight control tests) have been transported to their new home at the Flixton Aviation Museum in Norfolk – a fitting location for the Boulton & Paul machines, the originals of which were manufactured in Norwich and assembled at Mousehold Heath Aerodrome, on its outskirts.

For modellers this was also a “red letter” week as Airfix made good on its announcement of the release of a new Defiant kit in 1/72nd scale at the International Plastic Modellers Society annual international event at the Telford Exhibition Centre last November. The new kit series is finally released to the public this week.

Anyone involved with building plastic kits will remember the original Airfix Defiant, bagged and sold when this writer was but a child, and available in “Woolworths”. The kit suffered from some serious shape inaccuracies based upon poor source drawings and the then Airfix perchant for raised rivets. As one employee put it to me years ago the standard design brief at the time was “-and we must have lots of rivets, the kids love rivets…..” With those sort of problems this model kit has long been ripe for improvement, including a complete nose re-graft, done by many of us over the years.

The old Airfix Defiant could be made into a fair replica of its age but not without a complete rebuild of the nose, tail etc. This one used parts from Spitfire and Hurricane kits back in the 1970’s, including the grafting on of a Spitfire nose, Hurricane propeller and exhaust stacks and lots of filler. Built by Association Archivist Les Whitehouse

Nevertheless the model industry has moved on by leaps and bounds since those days and the new Defiant kit pays homage not only to the famous airframe but also to the latest techniques. The new kit used laser scanning techniques on the full size original, three dimensional CAD drawings and extensive research in addition to cross-referencing back to the original surviving drawings, photographs and maintenance manuals. The Association is proud to have been associated with the research involved in its creation via its archivist.

The top of the range is a “dogfight double” with glue and paints, covering the previously mentioned L7005, PS-B and Do17 5K+AR, the machine which has recently been raised and preserved by the RAF Museum. The basic Defiant kit on its own features PS-U L7013 of 264 squadron in the Battle of Britain (which survived the battle) and DZ-Z N3328 of 151 squadron (with sharkmouth), an aircraft frequently flown by ace Sgt Henry Bodien and his gunner Sgt D. E. O. Jonas . A third kit, defined as a starter kit (because it is supplied also with glue and paint) features N3333 YD-B 255 sqn when it was first being worked up in day fighter scheme.


From Graces Guide

1934 The aircraft building business was sold off by Boulton and Paul of Norwich, which continued to operate as a construction business Ώ] . The new company was listed as a public company.

Their Overstrand bomber was just entering service - it featured the world's first enclosed, power-operated turret, mounting a single Lewis gun and propelled by compressed air. The company licensed a French design of an electro-hydraulic four-gun turret which became a major feature of their future production. In addition to fitting turrets to bombers, Boulton Paul was to install them in fighters. Boulton Paul's chief aircraft designer was John Dudley North.

Over the next couple of years a new factory site was built up in Pendeford, Wolverhampton. This gave access to a large skilled workforce on top of the 600 or so employees that left Norwich for Wolverhampton. Even so Boulton Paul would later set up a training centre in Scotland to bring in extra workers. The first "turret" fighter to be built was the Hawker Demon.

This was followed by Boulton Paul's most famous aircraft, the Defiant, which was a revolutionary but flawed concept - a "fast" fighter with no fixed forward armament but a powerful four-gun dorsal turret.

The company produced 136 of the Blackburn Roc aircraft 1937-1940 under sub-contract, the company was responsible for the detail design of the revised Skua fuselage from the engine firewall back to the tail joint on the rear fuselage, including the BPA Type A Mk IIR gun turret and installation. Blackburn designed the rest of the airframe details including the revised wings.

Boulton Paul also built the Fairey Barracuda and did conversions of the Vickers Wellington. The only post-war design was the Balliol advanced trainer, of which 229 were built, including 30 as the "Sea Balliol" deck-landing trainer.

1937 Aeroplane constructors. ΐ]

Post-WWII: In the jet age, Boulton Paul worked on the English Electric Co Canberra and De Havilland Vampire. It designed and built a couple of delta-wing jet-engined aircraft for research work and continued to tender designs for official requirements.

1961 Aircraft designers and constructors. High precision engineers. Operate extensive aerodrome at Seighford, Nr. Stafford for aircraft final assembly and operational flying. 2,000 employees. Α]

1961 January. John Dudley North recommended to the Board that they consider a possible offer from his friend Sir George Dowty and join forces, so that BPA would become a member of the Dowty Group, the new title created the same year was just that:- “Boulton Paul Aircraft Ltd - Member of the Dowty Group”.

1970 The company name was changed to Dowty Boulton Paul Ltd. The company was by then a member of the Dowty Aerospace and Defence Group of companies.

1991 Dowty Boulton Paul, along with others was grouped again as Dowty Aerospace with the acquisition of the group by TI.

2000 TI sold the company to Smiths and becoming part of Smiths Actuation Systems Division in 2001.

2007 Smiths was acquired by GE in May 2007.

In September 2009 GE sold the actuation business of the former Dowty Aerospace at Pendeford Lane, nr. Wolverhampton to Moog but refused to sell them the factory and land it occupied. It is still unoccupied, while GE have carried out a number of environmental clean-ups. Moog operated from the site while it built a new factory on the I.54 development site off J2 of the M54 – moving there in 2012.

Boulton Paul was one of the two main innovators of gun turret designs for British aircraft, along with Nash & Thomson they supplied large numbers of installations for British aircraft. Boulton Paul's designs were largely based on originals licensed from the French company SAMM (Societe d'Application des Machines Motrices), while Nash & Thomson concentrated on the FN designs originated by the firm's co-founder, Archibald Frazer-Nash. Boulton Paul's turrets were electro-hydraulic in operation electric motors located in the turret drove hydraulic pumps that powered hydraulic motors and rams. This was more effective than electric motors alone, and did not require power developed by the aircraft's engines as did the hydraulic system utilized by the Nash & Thomson design. Production was transferred to Joseph Lucas Ltd. Β]


Defiant

War induces combatants to seek advantages by any means possible. In regard to World War II aircraft, the quest for an edge encompassed numerous aspects, such as size, bomb capacity, speed, rate of climb, altitude, maneuverability, and potency of armament. Even though the fundamental configurations of aircraft had been established by the end of World War I, the quest for an advantage in the air brought a spate of new variations into the sky. For every successful innovation, such as the radar-equipped all-weather fighter, there were interesting failures, such as the turret fighter and the lightweight interceptor. And for every evolved or carefully conceived design, there was a wartime improvisation that occasionally worked—though not always as originally intended.

The British should have known better than to develop the turret fighter. The two-seat fighter from which it evolved, the Bristol F.2B of 1917, had achieved its phenomenal success by being flown as a single-seater with a sting in the tail, rather than relying primarily on the rear gunner’s weapon. The F.2B’s successor in 1931, the Hawker Demon, differed little from it in armament, but the problems encountered by the gunner in handling a .303-inch gun in the open cockpit of an airplane flying at nearly twice the Bristol’s speed led the Air Ministry to seek a more advanced weapons system.

One solution to the problem was offered by Boulton Paul Aircraft Ltd., which had been subcontracted to build Demons for the RAF, and which had also obtained the rights to produce an electro-hydraulically operated turret—invented by French engineer Joseph Bernard Antoine de Boysson—capable of traversing 360 degrees and incorporating either a 20mm cannon or four .303-inch machine guns. After seeing the turret demonstrated in the nose of a Boulton Paul Overstrand bomber, the Air Ministry issued a specification for a fighter armed with four machine guns in the de Boysson turret and capable of flying as fast as the Hawker Hurricane fighter. Since Hurricanes were expected to protect the turret fighter from enemy fighters while it attacked enemy bombers from the side or below, the specification limited armament to the turret. Such a measure saved weight, but in essence it made the pilot nothing more than a chauffeur for his gunner—hardly a role that went over well with aggressive fighter jockeys.

Designed by John Dudley North, the Boulton Paul Defiant was a commendably clean and compact airplane, powered by the same 1,030-horsepower Rolls-Royce Merlin III engine used in the Hurricane and the Supermarine Spitfire. A retractable fairing helped to smooth the airflow behind the rear turret when it was not in use, and in spite of the drag that the turret still imposed on it—as well as a gross weight of 8,600 pounds compared to the Hurricane’s 6,218—the Defiant managed a maximum speed of 302 miles per hour at 16,500 feet compared to the Hurricane’s 316. It took the Defiant 11.4 minutes to climb to that altitude, however, whereas the Hurricane could reach it in only 6 1/2 minutes. First flown on August 11, 1937, the Defiant was approved for production, but because Boulton Paul was then relocating from Norwich to a new plant at Wolverhampton, the first operational Defiants were not deployed with No. 264 Squadron until December 1939. When the Germans invaded the Low Countries on May 10, 1940, the unit moved from its training base at Martlesham Heath to Duxford from there, A Flight flew to Horsham Saint Faith and B Flight returned to Martlesham, where it would operate alongside the Spitfires of No. 66 squadron.

The Defiants did their intended job fairly well in their first combat. On May 11, No. 264’s commander, Squadron Leader Philip A. Hunter, and Pilot Officer Michael H. Young flew an evening convoy patrol as far as the Happisburgh lighthouse. The next day Flt. Lt. Nicholas G. Cooke led A Flight on a patrol off the Dutch coast, accompanied by six Spitfires of No. 66 Squadron. They soon encountered enemy aircraft, and the Defiants drew first blood five miles south of The Hague as a Junkers Ju 88A fell victim to Hunter and his gunner, Sgt. Frederick H. King, while a second was claimed by Young and Leading Aircraftman Stanley B. Johnson. Cooke added a third victory to the squadron’s opening tally when he caught an He 111 six miles south of The Hague and his gunner, Cpl. Albert Lippett, shot it down.

On the following morning, six Defiants of B Flight, accompanied by six Spitfires of 66 Squadron’s A Flight, were flying another sweep over the Dutch coast when they spotted Junkers Ju 87Bs dive-bombing a railway line and attacked. Between them, the British claimed ten of the Stukas—four of which were credited to the Defiants—before themselves coming under attack by Messerschmitt Me 109Es of the 5th Staffel of Jagdgeschwader 26. Flight Lieutenant Kenneth McLeod Gillies, a Spitfire pilot who had shot down a Stuka east of Rotterdam, damaged an Me 109 before 66 Squadron disengaged. One Spitfire fell victim to Ltn. Hans Krug, but its pilot managed to force land his damaged plane in Belgium.

The fight had a much grimmer outcome for 264 Squadron. In their first encounter with enemy fighters, the six Defiant crews found themselves unable to evade the Me 109s, and five were shot down in short order, although only one German, Fw. Erwin Stolz, identified his adversary as a Defiant at the outset the other victors—Ltn. Eckardt Roch (who claimed three), Leutnant Krug, Uffz. Hans Wemhöhner, and Fw. Wilhelm Meyer—all claimed Spitfires, before subsequently learning the true identity of their adversaries. The sole Defiant pilot to return, Pilot Officer Desmond Kay, claimed that five German fighters went down in the course of the massacre, and they were duly credited to the squadron.

In actuality, the Defiants had managed to shoot down only one of their assailants, who—contrary to popular misconception—already knew what he was up against and fell victim to overconfidence, rather than from mistaking the turret fighter for a single-seater. As Ltn. Karl Borris himself recorded it in his diary:

Enemy contact with a mixed British formation . . . I bank toward a Defiant, I can clearly see the four machine guns in its turret firing however, I do not think they can track me in a dogfight. I approach closer, and open fire at about seventy meters range. At this moment, something hits my aircraft, hard. I immediately pull up into the clouds and examine the damage. The left side of my instrument panel is shot through a round had penetrated the Revi [reflex gunsight] and a fuel line has obviously been hit—the cockpit is swimming in gasoline. The engine coughs and quits, starved of fuel. I push a wing over and drop from the clouds. Unbuckle, canopy off, out!

Borris parachuted onto a dike wall near the mouth of the Rhine River and made his way back to 5./JG 26 four days later. Having lived to profit from this reminder of the price one pays for cockily dismissing any armed opponent, he would survive the war with forty-three victories.

For the next ten days, No. 264 Squadron refrained from operations, but on May 23, its Defiants joined in the RAF’s desperate effort to cover the evacuation of Allied troops from Dunkirk. By the end of the month, the squadron had claimed forty-eight victories—thirty-seven on May 29 alone—but lost nine planes, including that of Cooke and Lippett, killed on the thirty-first. Occasionally, the Defiant’s superficial resemblance to the Hurricane did mislead German fighters into attacking it from the rear, with sometimes fatal results for the attackers. Soon the Germans learned to distinguish between the Defiant and its single-seat stablemates, however, with results that spoke for themselves. A second Defiant unit, No. 141 Squadron, had a disastrous combat debut on June 28, when nine of its planes tangled with Me 109Es and lost seven while claiming only four victories. On July 19, nine more Defiants of 141 Squadron encountered Me 109Es of JG 51 and again lost seven planes, while one of the two surviving crews, Flt. Lt. Hugh N. Tamblyn and Sgt. S. W. N. “Sandy” Powell, claimed one of the enemy in return. In August the Defiant units’ air bases were moved farther north, but the RAF’s need for anything which could fly and fight at that time kept them engaged—and suffering mounting losses. By late 1940, the Defiant Mark Is were being relegated to the night-fighting role, and a radar-equipped version, the Defiant Mark II, was introduced. As such, they did well, being in fact the most successful night fighters of 1941 until sufficient numbers of Bristol Beaufighters and de Havilland Mosquitos became available to phase them out of first-line service.


Early RAF Gun Turrets

Post by Robert Hurst » 04 Apr 2003, 14:34

The Westland Pterodactyl Turret

Given the fact that hostile aircraft usually attacked from the rear, where the tailpane usually impeded the field of defensive fire, Westland designed a two-seat fighter with a maximum field of fire against an attack form the rear. This was the tailless Pterodactyl Mk.V of 1932.

Painted to resemble its prehistoric namesake, the single-seat prototype of an earlier Pterodactyl was flown at air shows, providing light entertainment for the crowds, but the Mk.V two-seat fighter was a studied attempt to revolutionise the accepted concept of fighter design. Designed with the assistance of Professor G.T.R. Hill, the new fighter was to be armed with two Lewis guns which could cover the whole rear hemisphere, the pilot being provided with a fixed, forward-firing Vickers gun. The turret was mounted directly behind the pilot, supported by ball-bearings running in a ring fixed to the aircraft structure.

The turret was powered by a 24 volt electric motor fed from a generator driven by the engine or a windmill-type generator with a battery back-up unit. When the turret was being used the motor ran continuously, power being taken off when required from a gearbox containing two infinitely variable disc and roller friction-type take-offs.

From the gearbox, shafts carrying worm gears engaged in teeth on the outer rim of a circular frame to which the guns were fitted. The turret was rotated in azimuth by a pinion meshing into internal teeth cut into the fixed ring. The gunner controlled the speed and direction of turret rotation via a handle which applied power from the gearbox by way of bellows chambers and hydraulic tubes. The motor stored sufficient kinetic energy for any sudden acceleration, and eliminated the initial sluggishness of a directly coupled motor. Motion of the handle forwards or backwards elevated the guns and sight arm, and a sideways movement rotated the turret in the same direction. Spare drums for the Lewis guns were contained in a U-shaped dispenser - when an empty drum was placed into one side of the container, a full drum was automatically unlocked from the other side ready for use.

Unfortunately the Pterodactyl fighter turret did not get beyond the experimental stage, and there are no records of it being air-tested. One reason was probably the variable disc and roller transmission system which, although it was thought to be an ideal method of transmission, was rejected by both Bristol and Boulton Paul after early experiments with turret drives.

The above text and photos were taken from "British Aircraft Armament Vol.1: RAF Gun Turrets", by R Wallace Clarke.

Post by Robert Hurst » 04 Apr 2003, 15:20

The Handley Page Heyford, designed in 1927, was fitted with a retractable under defence turret, known for obvious reasons as the Dustbin. Armed with a Lewis gun on a flexible mounting, it was wound down into position under the big biplane bomber. The gunner then lowered himself on to a small seat. The gun was fitted to a tubular arm low to his front. He could rotate the enclosure round to each beam, giving him a reasonable field of fire to counter an attack from below, and spare ammunition drums were stowed in the fuselage within reach. Gunners reported that the position was very cramped, and when facing aft there was a blustering draught. When turned to the beam position slipstream interference was negligible.

The Barnes Wallis Windmill

The Aircraft Division of Vickers-Armstrongs submitted a design in 1934 for a biplane light bomber. This aircraft the Vickers G.4/31, was chosen from eight competing designs, but was later rejected in favour of the Wellesley monoplane bomber made by the same company. The G.4/31 featured a primitive powered turret in the rear cockpit, driven by a slipstream-operated power unit.

The mounting concisted of an L-shaped body fixed at the base to a rotatable ring. The windvane motor turned a flywheel which powered a flexible drive through a friction clutch. The gunner selected the speed and driection of rotation by means of a finger dialling mechanism. The dial operated a differential gearbox which drove a pinion meshed with the rotating ring of the turret. If the dial was turned to the left on the first hole, the turret would revolve slowly anti-clockwise, dialling fully to the right rotated the turet quickly to the right. There was provison for oxygen supply, gun and clothing heating and an intercom jack plug, the electrical services being fed through brush gear from the fixed ring. The single Lewis gun was fitted to an arm at the top of the main turret frame, being manipulated in elevation by hand. Wallis devoted much time and attention to the design, which was said to work quite successfully.

As with the Westland turret, the Vickers design was not accepted for Service use, but was significant as being another step in power assisted aircraft manipulation.

The above text and photos were taken from "British Aircraft Armament Vol.1: RAF Guns and Turrets", by R Wallace Clarke.

Post by Robert Hurst » 05 Apr 2003, 10:41

The Armstrong Whitworth Turret - Pt 1

In the early 1930s, the Sir W.G. Whitworth Aircraft Company was among the leading producers of aircraft for the Royal Air Force. In 1932 the company was working on a design for a new monoplane bomber transport aircraft powered by two Armstrong Siddeley Tiger engines, the AW.23. When the defensive armament system was discussed, it was decided that the gunners would have to be protected from the slipstream. In common with most manufacturers at this time, it was realised that with increased operating speeds it was becoming difficult to control free mounted defensive guns in open cockpits. The Bristol Company had just produced a totally enclosed manually operated turret for their Type 120 biplane, but this was merely a glazed cupola fitted over a standard Scarff ring, and was never produced in quantity.

It was decided that a purpose-made turret would have to be designed for the AW.23, suitable for installation in the nose and tail positions of the new aircraft. A small turret development unit was formed, and in nine months a prototype was ready for ground firing tests. The tests revealed a faulty gun mounting bracket, but this was soon rectified and the turret was mounted in an Atlas biplane for air testing. Armed with a single Lewis gun, the turret was suspended on rollers in a vertical track, and was turned by the reaction of the gunner's feet on a ribbed rubber floor covering. The main feature of the new turret was the gun elevation control this was an ingenious mechanism which balanced the weight of the seated gunner with his gun. There was also a following link system which ensured that the gunner,s eye was always in line with the gunsight throughout all angles of elevation. The designers also achieved a remarkable range of vertical movements - from an upward limit of 87 degrees the gunner could by standing and leaning forward over the front overhang, engage targets almost directly below him. The company claimed that merely by leaning forwards or backwards the gun could be depressed or elevated, and the whole mechanism gave accurate gun control during any evasion manoeuvres carried out by the pilot. Although the turret could be locked in any positoin of traverse or elevation, the gunner could fire whilst moving the turret without any problems of recoil or excessive vibration. When firing to the beam, the force of the slipstream on the barrel tended to rotate the cupola to the rear. To help overcome this, two balancing vanes were fixed to the top rear framing, but even then, firing to the beam required string hands and legs.

The 7.7 mm (0.303 in) Lewis Mk III gun was sighted by either a 114 mm (4.5 in) ring and bead sight, or a Norman Vane-type speed compensating sight. Five 97-round magazines were carried, spare magazines being clipped to the inside wall of the turret within easy reach of the seated gunner. The gunner entered the turret from the rear fuselage and stepped into a tip-up type seat. Later gunnery training models were fitted with bicycle-type seats made by Terrys Ltd, which, as some ex-gunners recall, were not the most comfortable mode of air travel. The dome shaped cupola consisted of a welded metal framework which housed panels made of Rhodoid acrylic plastic material.

The air firing tests were so promising that the company decided to take out a patent. This was dated November 1933, and details were then circulated to other manufacturers. A sister company, A.V. Roe Ltd, became interested in the turret and decided to use it to arm their new reconnaissance bomber, the Anson.

The Armstrong Whitworth AW.23 did not reach production, but the design was used for the famous Whitley, which was fitted with the turret in the nose and tail positions. Although the Whitley was eventually re-armed with Nash and Thompson power operated turrets, the AW turret saw limited service with Anson aircraft in the early war period. Its main use however was for gunnery training in Ansons and Airspeed Oxford aircraft.

The above text and photos were taken from "British Aircraft Armament Vol.1: RAF Gun Turrets", by R Wallace Clarke.

Post by Robert Hurst » 05 Apr 2003, 11:20

The Armstrong Whitworth Turret - Pt 2

When the first Ansons and Whitleys entered squadron service, air firing training commenced, with gunners firing at towed drogue targets. After the cold and draughty open gunner's cockpits, the turrets were very popular with the gunners and the usual cumbersome and heavy clothing was soon discarded: this fact alone contributed to a higher accuracy of gunnery. As the gunners mastered the new technique, accuracy improved even more, but reports of accidental damage to the host aircraft became more frequent than was usual when using the Scarff ring-mounted guns. Some Ansons were returning from air firing exercises with bullet-riddled tail surfaces and wings. An enquiry found that the traversing mechanism was so smooth that it was very easy to overrun when traversing on to a target, and also that when the gun was fired the vibration tended to turn the turret, with the help of the force of the slipstream on the barrel, towards the tailplane. With this in mind, gunners were instructed to avoid the tailplane area until guard rails could be installed. This edict applied only to training: in the event of of hostilities the tailplane would have had to take its chances, as it would be precisely this area where the enemy would be pressing home his attacks. The turret had an all-round traverse of 360 degrees when mounted on Anson and Oxford aircraft on the Whitley installation the field of fire was limited by the fuselage to 85 degrees to each beam.

The de Havilland Don and AW.29 prototypes were also fitted with the turret, and the Royal Navy ordered a large number to arm motor torpedo boats and patrol craft, in which it was found to be an ideal weatherproof gun mounting and lookout position.

The Armstrong Whitworth turret was probably the most efficient hand-operated aircraft gun turret in service in the early 1930s, but several other companies were developing electrical, pneumatic and hydraulically powered designs which were to revolutionise bomber defence in the next decade.

The above text was taken from "British Aircraft Armament Vol.1: RAF Gun Turrets", by R Wallace Clarke.

The photos in this section were taken from "Armament of British Aircraft 1909-1939", by H F King.

Post by Robert Hurst » 08 Apr 2003, 11:34

Early Boulton Paul Aircraft Gun Turrets - Pt 1

Boulton & Paul's first essay into unusual aircraft armament is linked with the company's design for a 'bomber destroyer', in the shape of the Boulton & Paul Bittern. This consisted of two Lewis guns mounted in trunnions, one either side of the front fuselage so that they could rotate in the vertical plane. They were remotely controlled by the pilot, who aimed the guns by a sight which was linked with the movement of the guns in elevation. The Bittern was not accepted for production, but the novel armament installation marked the beginning of the company's involvement in this importamt field of military aviation.

In 1927 the prototype of a new high-performance bomber, the Sidestrand, flew from the company's airfield at Mousehold near Norwich. This aircraft, which was contemporary with the Fairey Fox, had a speed and performance equal to any of the fighters in RAF service. The defensive armament consisted of the usual Lewis guns mounted on Scarff rings, fitted to open gunners' positions, and a Lewis in an under defence position. Successful trials were carried out leading to a production order for 20 aircraft, which were destined for No.101 Squadron based at Bircham Newton. The squadron air crews were delighted with their new equipment, and proceeded to show many intercepting fighters a clean pair of heels during mock interceptions. The only problem seemed to be with the air gunners, for with the higher operating speeds it was found to be more difficult to manipulate the Lewis guns in the stronger slipstream. The open cockpit of the nose position in particular was proving very uncomfortable in low temperatures, and changing ammunition drums with cold, heavily gloved hands was very difficult, some of the drums even being lost overboard, damagng propellers and aircraft structure.

After persistent reports of the poor marksmanship of Sidestrand gunners, the Air Staff accepted the fact that the problem lay in the increased speed of the new bombers. Consequently Boulton & Paul were awarded a development contract to provide some means of protection for the nose gunners. J D North had attended various armament courses during the war and was not inexperienced in the complexities of air firing, and he was ably assisted by H A Hughes, who took a leading part in the project. It was decided that the only practical solution would be a totally enclosed power-assisted turret. This was to be an historic decision, marking the company's entry into the field of specialised armament projects, in which it was to take a leading role in future years.

It was decided to provide a fully glazed, cylindrical turret with domed ends, which would fit into the nose of the aircraft. Various electrical and hydraulic power systems were tried, but the best power-to-weight performance seemed to be given by a pneumatic system. A reversible compressed-air motor was mounted behind the turret, rotating it by means of a geared drive in the bottom mounting. Side loads were taken by a circular rail amidships, supported by rollers in the fuselage.

The turret was armed with a single Lewis mounted on a pivoted arm. Control of the gun in elevation and depression was manual, but the gunner and gun mounting were supported by an ingenious hydraulic balancing mechanism. The gunner's seat was supported by a hydraulic ram, connected to a pair of smaller rams coupled to the gun arm. The rams were so designed that the gunner and mounting were balanced - if the gun was aimed upwards the rams lowered the seat, giving a comfortable sighting and firing position. When firing downwards the rams connected to the gun arm raised the gunner's seat to a position which enabled him to bring the guns to bear on the target. The gun barrel protruded through a vertical slot extending from top to bottom of the turret front, which was sealed from the slipstream by a zip-fastener mechanism fixed to rubber side facings.

The turret was traversed by the pneumatic motor, controlled by valves actuated by sideways pressure of the gun. Mounted on a pivot, the gun had limited sideways movement, and when moved to the limit the gun actuated a spring-loaded plunger, which operated a pneumatic valve which admitted compressed air to the motor. Further pressure on the gun handle opened the valve further, increasing the movement of the motor and the turret, while movement of the spade grip in the opposite direction opened another valve and rotated the turret in the reverse direction. The turret could be rotated a full 360 degrees in either direction if the gun barrel was sufficiently elevated to clear the fuselage. With the gun below this position traverse was limited by cut-out valves, which cut off pressure before the gun barrel reached the fuselage.

The compressed-air supply was stored in bottle to a pressure of 8.4 kg/sq cm (120 lb/sq in). As pressure was used the bottles were recharged by a compressor on the starboard engine. One of the problems faced by the designers was the need to provide a position for bomb aiming inside the turret. The front half of the turret was extensively glazed, one large section being made to open outwards and lock into a position where a bomb sight could be used. This was on the port side of the cupola, and when the bomb sight was used the turret was locked into a central fore and aft position.

After a series of tests at Boscombe Down the Air Ministry issued an order, to specification 29/33, for enough of the new turrets to equip two squadrons of Sidestrands, which were then to be known as Sidestrand Vs. Several other modifications were also called for: the undercarriage was stengthened, and the Bristol Jupiter engines were replaced with more powerful Bristol Pegasus IIM3s. After these modifications were carried out the name of the aircraft was changed to Overstrand. The first conversion was carried out on Sidestrand (J9186), which became the prototype Overstrand. On 22 February 1933 (J9186) was flown to Bircham Newton for service trials, during which various problems were found, and the aircraft was flown back to Norwich for modifications on 19 March.

On 30 June 1934 the underlying conflict between the flourishing woodworking department and the aircraft side of the business came to a head. After protracted and often acrimonious meetings it was decided to form two separate companies. The woodworking deparment would remain in the existing works, and the aircraft side was taken over by a newly formed company chaired by the Rt Hon Lord Gorell and Viscount Sandon. More significant was the appointment of the dynamic John North and S W Hiscocks as joint Managing Directors.

A new purpose-built factory was to be built at Wolverhampton, and in the meantime aircraft production continued in leased premises in Norwich. The new company was to be known as Boulton Paul Aircraft Ltd, a name which was to make an impact on the aviation industry. Problems with the Overstrand and its turret took longer to sort out than at first thought, but on 24 January 1935 Overstrand (J9185) landed at Bicester, where No.101 Squadron was then based. Overstrands gradually replaced Sidestrands and proved popular with the crews, squadron gunners in particular being full of praise for the comfort and ease of gun manipulation. Seated in a draught-free, heated enclosure with power assisted gun training, gunners acieved a hit rate of 55% against towed targets, compared with an average of 15% by gunners using Scarff rings in open cockpits.

The Overstrand turret received world-wide publicity, being hailed as a pointer to future bomber armament, which indeed it was. The Nash and Thompson hydraulic system was still in the development stage at this time. Various high-ranking officers from the RAF and foreign air forces visited No.101 Squadron at Bicester, many keen to try out the new turret mechanism. One distinguished officer insisted on installing himself inside the turret to test the controls. After closing the door he grasped the spade grip of the Lewis gun and pressed it to one side, and the turret immediately started to rotate at full speed. The unfortunate gentleman became disorientated, but onlookers could do nothing to help until the air pressure was exhausted, and the nauseated officer was then extricated. This incident was not so amusing to Boulton Paul as the highly colourful description related in the mess after the visitors had left. It highlighted the major drawback of the system, that every spell of sustained action had to be followed by a period of rest to allow the compressor to recharge the bottles - a situation unlikely to instil confidence in gunners likely to be under continuous attack. To sustain an adequate supply it was found that the compressor and air bottles would have to be too large to be practicable, and although the Overstrand continued to give good service it was decided to re-examine other means of powered gun control.

Meanwhile the transfer of plant and machinery to the Pendeford Lane works at Wolverhampton was completed in 1936 and the first aircraft produced in the factory began to emerge from the production bay. They were Haweker Demon two-seat fighters, in which ironically the company's competitors were to fit their new FN.1 powered gun turret. The aircraft were flown into the Parnall airfield at Yate. where the turrets were fitted into the specially prepared rear cockpits.

The above text and first two photos were taken from "British Aircraft Armament Vol.1: RAF Gun Turrets", by R Wallace Clarke. The bottom photo was taken from "Armament of British Aircraft 1909-1939", by H F King.


Aircraft

History

At first, guns on aircraft were either fixed in orientation or mounted on pedestals or swivel mounts called pintles.. The latter evolved into the Scarff ring, a rotating ring mount which allowed the gun to be turned to any direction with the gunner remaining directly behind it. As aircraft flew higher and faster, the need for protection from the elements led to the enclosure or shielding of the gun positions, as in the "lobsterback" rear seat of the Hawker Demon biplane fighter.

The first bomber in the Royal Air Force to carry an enclosed power-operated turret was the Boulton & Paul Overstrand twin-engined biplane, which first flew in 1933.

The Overstrand was similar to its First World War predecessors in that it had open cockpits and hand-operated defensive machine guns. However, unlike its predecessors, the Sidestrand could fly at 140 mph (225 km/h) making operating the exposed gun positions difficult, particularly in the aircraft's nose. To overcome this problem, the Overstrand was fitted with an enclosed and powered nose turret mounting a single Lewis gun. As such the Overstrand was the first British aircraft to have a power-operated turret. Rotation was handled by pneumatic motors while elevation and depression of the gun used hydraulic rams. The pilot's cockpit was also enclosed but the dorsal and ventral gun positions remained open, though shielded. [18] The American Martin B-10 all-metal monocoque monoplane bomber introduced turret-mounted defensive armament within the United States Army Air Corps, almost simultaneously with the RAF's Overstrand biplane bomber design. The Martin XB-10 prototype aircraft first featured the nose turret in June 1932 — roughly a year before the less advanced Overstrand airframe design — and was first produced as the YB-10 service test version by November 1933. The production B-10B version started service with the USAAC in July 1935.

In time the number of turrets carried and the number of guns mounted increased. RAF heavy bombers of World War II such as the Avro Lancaster and Handley Page Halifax and Short Stirling typically had three powered turrets, with the rear one—the tail gunner or "Tail End Charlie" position—mounting the heaviest armament of four 0.303 inch Browning machine guns or, late in the war, two AN/M2 light-barrel versions of the American Browning M2 machine gun as in the Rose-Rice turret.

During the World War II era, British turrets were largely self-contained units, manufactured by Boulton Paul Aircraft and Nash & Thomson. The same model of turret might be fitted to several different aircraft types. Some models included gun-laying radar that could lead the target and compensate for bullet drop.

The UK introduced the concept of the "turret fighter", with aeroplanes such as the Boulton Paul Defiant and Blackburn Roc where the armament (four 0.303 inch) machineguns was in a turret mounted behind the pilot, rather than in fixed positions in the wings. The concept came at a time when the standard armament of a fighter was only two machine guns. In the face of heavily armed bombers operating in formation, it was thought that a group of turret fighters would be able to concentrate their fire flexibly on the bombers making beam, astern and from below attacks practicable.

Although the idea had some merits in attacking bombers, it was found to be impractical when dealing with other fighters the weight and drag of the turret impaired the airplane's speed and maneuverability relative to a conventional fighter which the flexibility of the turret armament could not compensate for. At the same time conventional fighter designs were flying with 8 or more machine guns. Attempts to put heavier armament (multiple 20 mm cannon) in low profile aerodynamic turrets were explored by the British but were not successful.

Not all turret designs put the gunner in the turret along with the armament. Both the Americans and Germans produced aircraft with remote controlled turrets. In the US, the large, purpose-built Northrop P-61 Black Widow night fighter was produced with a remotely operated dorsal turret that had a wide range of fire though in practice it was generally fired directly forward under control of the pilot. For the last Douglas-built production blocks of the B-17F (the "B-17F-xx-DL" designated blocks), and for all versions of the B-17G Flying Fortress a twin-gun remotely operated "chin" turret, designed by Bendix and first used on the experimental YB-40 "gunship" version of the Fortress, was added to give more forward defence. Specifically designed to be compact and not obstruct the bombardier, it was operated by a swing-away diagonal column possessing a yoke to traverse the turret, and aimed by a reflector sight mounted in the windscreen.

The intended replacement for the German Bf 110 heavy fighter, the Messerschmitt Me 210, possessed twin half-teardrop-shaped, remotely operated Ferngerichtete Drehringseitenlafette FDSL 131/1B turrets, one on each side "flank" of the rear fuselage to defend the rear of the aircraft, controlled from the rear area of the cockpit. By 1942, the German He 177A Greif heavy bomber would feature a Fernbedienbare Drehlafette FDL 131Z remotely operated forward dorsal turret, armed with twin 13mm MG 131 machine guns on the top of the fuselage, which was operated from a hemispherical, clear rotating "astrodome" just behind the cockpit glazing and offset to starboard atop the fuselage — a second, manned powered Hydraulische Drehlafette HDL 131 dorsal turret, further aft on the fuselage with a single MG 131 was also used on most examples.

The US B-29 Superfortress had four remote controlled turrets, comprising two dorsal and two ventral turrets. These were controlled from a trio of hemispherically glazed gunner-manned sighting stations operated from the pressurised sections in the nose and middle of the aircraft, each housing an altazimuth mounted pivoting gunsight to aim one or more of the unmanned remote turrets as needed, in addition to a B-17 style flexible manned tail gunner's station.

The defensive turret on bombers fell from favour with the realization that bombers could not attempt heavily defended targets without escort regardless of their defensive armament unless very high loss rates were acceptable, and the performance penalty from the weight and drag of turrets reduced speed, range and payload and increased the number of crew required. The British de Havilland Mosquito light bomber was designed without any defensive armament and used its speed to avoid engagement with fighters, much as the minimally armed German Schnellbomber aircraft concepts had been meant to do early in World War II.

A small number of aircraft continued to use turrets however—in particular maritime patrol aircraft such as the Avro Shackleton used one as an offensive weapon against small unarmoured surface targets. The Boeing B-52 jet bomber and many of its contemporaries (particularly Russian) featured a tail-mounted barbette (a term from British English), or "remote turret" —an unmanned turret but often with more limited field of fire.