Boulton Paul P.75 Overstrand

United Kingdom (1933)

Medium Bomber – 28 Built

A flight of five No.101 Squadron Overstrands. (Boulton Paul Aircraft Since 1915)

The Boulton Paul P.75 Overstrand was a two-engined biplane that became the RAF’s mainstay bomber aircraft in the early to mid 1930s. The Overstrand was an improvement upon the earlier P.29 Sidestrand biplane bombers after the type recieved several criticisms regarding the frontal gunner position being exposed to the elements on such a high speed aircraft. To amend the complaints, Boulton Paul would design a modified version of the Sidestrand that would use a fully-enclosed powered turret, which would be revolutionary for the time. To test the design, three Sidestrands would be converted into Overstrands. The Overstrand would equip No.101 squadron and 25 newly built Overstrands would be constructed. Aside from mainline service, a number were experimentally modified by Boulton Paul, such as receiving different turret arrangements and more powerful engines. By the time of the Second World War, the aircraft had become obsolete, as new monoplane bombers entered production and replaced it. The type would continually fly in limited numbers for training and auxiliary purposes, but by 1941 would be considered obsolete and grounded.

Boulton & Paul and the Sidestrand

The Boulton & Paul P.29 Sidestrand was a modern and aerodynamic aircraft of the time. But while it was fast it had several glaring flaws, the biggest being the open front turret which exposed the gunner to high speed winds and cold air. (Boulton Paul Aircraft Since 1915)

In the mid 1920s, the Boulton & Aircraft company was beset by hard times. The company was surviving off of small orders for prototype aircraft and was in a rough financial state. The company had, up to this point, focused on creating twin-engine biplane bombers, starting with the Bourges in the First World War and going to their latest of the time, the P.25 Bugle. In late 1925, their savior would be their newest twin bomber design; the P.29 Sidestrand. It was an all-metal, twin-engine biplane bomber with extensive work done into designing its aerodynamic fuselage, creating an innovative and sleek-looking aircraft for the time. Production was soon ordered and 18 were built. This new bomber would populate the No.101 squadron, the only bomber squadron the RAF was operating at the time. Despite its success, a problem began to arise with the forward gunners of the aircraft. The Sidestrand, thanks to its aerodynamic design and powerful Bristol Jupiter engines, was able to achieve a top speed of 140 mph (225 km/h). While this speed made the twin engine bomber quite a fast aircraft for the time, this luxury was not so appreciated by the front gunners of the aircraft, who had no means of protection against the strong slipstream in their open cockpits. The strong winds made aiming the Lewis gun difficult, as it was blown around, and even reports of the propellers being hit by drum magazines thrown from the position were growing to be common. This was not to mention the extreme cold the gunner had to endure as well. Frozen fingers were another common complaint from Sidestrand gunners. While the Sidestrands began to take to the air (and torment their front gunners), Boulton & Paul set to procure more production orders of the type over the 18 that were built, but no further production was ordered, mostly due to the worldwide recession. In the early 1930s, many current fighters of the time were experiencing the same slipstream issues as the Sidestrand was. The Air Ministry put out an order on December 28th, 1932 to seek design reworks that would fix this now commonplace issue with the Sidestrand. While many of the other aircraft would seek simple means, the issue with the gunner position on the Sidestrand was more complex and would require more work put into redesigning the aircraft. Ultimately, Boulton & Paul would decide the answer was a completely covered turret. The company had been working on such a design with their P.70 aircraft concept.

The P.70 was a concept aircraft that was based off the P.64 mailplane and used components of the Sidestrand. While it was never built, it had an innovative enclosed nose turret that the Overstrand would use. (Boulton Paul Aircraft Since 1915)

The P.70 was a twin-engine biplane bomber design based on their earlier P.64 mailplane and incorporated aspects of the Sidestrand. In the nose of the P.70 was a fully enclosed, cylindrical turret that was fully powered via compressed air. The turret would have a single gun mounted that elevated and depressed down a vertical split in the design. It would also have 360 degrees of rotation as long as the gun was elevated 70 degrees to allow it to lift over the nose of the aircraft. Ultimately, the P.70 was not selected for the competition it took part in, but the innovative turret design was chosen to be used on the reworked Sidestrand. In addition to making the front gunner more comfortable, other additions were made for the rest of the crew. The rear gunner had a new windshield installed behind his back to protect him from the fast winds, and the pilot now sat in a fully enclosed cockpit. Even further, the aircraft would implement an onboard heating system, taking off excess heat from the engine intakes. Other planned changes to the design were the wings being swept at the outer edges to compensate for the weight of the front turret, and structurally integrity was also improved in the hull of the aircraft to allow for a bigger bomb load. With the improved design finalized, it was chosen that the first aircraft to test this new design, at this point called the Sidestrand V, would be created by modifying a Sidestrand III; J9186. The order for the creation of the prototype would be 29/33.

Design

The Boulton Paul P.75 Overstrand was a twin-engined biplane bomber designed to improve the performance and crew comfort of the Boulton Paul P.29 Sidestrand. The airframe of the aircraft was of all-metal construction. The fuselage had a length of 46ft 11in (14.3 m). The wings of the aircraft were all-metal, 3-bay biplane wings. The wings themselves had an additional outer edge sweep to them, a design choice not found on the Sidestrand. This was to counter the increased weight of the nose due to the powered turret. The aircraft would have a wingspan of 71ft 11 in (29.2 m). Both the upper and lower wings would be built with ailerons. Mounted between the wings were two 580 hp Pegasus II.M.3 engines connected to two 4-bladed metal propellers. The engines were housed in nacelles that also carried a 17 gallon fuel tank, priming pumps, hand-stating magnetos and a gas starter. The very first Overstrand, which was converted from a Sidestrand, was equipped with 555 hp Pegasus I.M.3 engines. Covering the engine cowlings were 9-sided Townend rings. These assisted with improving the airflow of radial engines, reducing drag and increasing the overall speed of the aircraft. Connected to the engine nacelles on each side were the main connectors for the landing gear, which were each supported by struts. The Overstrand had large, rubber wheels that were bigger than those on the Sidestrand. The cockpit was located in front of where the wings connected to the main body. The cockpit itself was fully-enclosed with a sliding hood, a feature not present on the Sidestrand. The cockpit was glazed with anti-glare perspex. For the pilot, an autopilot was equipped, a feature also found in the Sidestrand. This was located directly behind the pilot’s seat. Behind the cockpit were two gunner positions near the middle of the airframe, one ventral and one dorsal. The dorsal firing position had a windshield installed to protect the gunner from the high speeds the aircraft would encounter. The ventral position would not have to deal with the rough winds due to the way it was positioned within the fuselage. The ventral gunner would also operate several pieces of equipment, including an F.8 camera, and a wireless set consisting of a T.1083 wireless transmitter, a R.1082 wireless receiver and a T.R.11 wireless transmitter/receiver. On the converted Sidestrands, they would continue to use the T.73 transmitter and R.74 receiver they came standard equipped with. Extra ammo magazines were availablefor all gunners. For crew communication, there was a telephone system installed that connected each of the crew members. For crew comfort, a heating system was equipped in the interior of the aircraft. Each crew member was able to appreciate the benefits of this system, no matter where they were located. Heat was siphoned from the Townend rings and engine cowlings through a series of ducts into the interior of the aircraft. Care was taken to make sure these ducts were clear of objects or debris when the system was activated, otherwise they would be forcefully ejected from the vents. At the tail end of the aircraft was a 9 inch by 5 inch tail-wheel, which replaced the landing skid of the Sidestrand. The vertical and horizontal stabilizers remained largely the same as how they were on the Sidestrand, but the rudder of the aircraft was lengthened. The Overstand also retained a rudder extension that was present on the Sidestrand. The horizontal stabilizers were supported by two struts on each side that connected to the fuselage.

A view of the prototype’s nose. On later models, the turret would be widened for increased crew comfort. (Boulton Paul Aircraft Since 1915)

The most innovative technical feature of the Overstrand was the powered turret at the nose of the aircraft. The turret design was created by H A Hughes, head of Armaments Section for Boulton & Paul. The design itself was originally part of the P.70 aircraft design, but with that project being canceled, the turret was reused on the Overstrand. The turret was cylindrical in shape, with the top and bottom being rounded. The majority of the turret was covered in Perspex to allow optimal viewing for the gunner, with the rest of the turret and frame being made of metal. The powered aspect of the turret came from pneumatic power from compressed air that was held in bottles. Each bottle was held at 200 Ib/sq and fed into the turret by an engine-powered air compressor at 40 Ib/sq. These bottles were rechargeable via the compressor and, at their full, could allow a total of 20 complete rotations of the turret before being exhausted. The turret itself was capable of 240 degrees of rotation with the gun pointing forward, and a complete 360 degrees if the gun was raised by 70 degrees. The turret was held on ball-bearings with brackets connected to the bottom and top longerons of the airframe. The top longerons in particular ended in a circular design that allowed rollers to rotate. The air was fed into the base of the turret, which was the main mechanism that rotated the turret. The armament of the turret was a single .303 Lewis machine gun, mounted to a mechanism that the gunner would use. The gun would protrude from a vertical slit at the front of the turret that allowed it to elevate. To protect this slit, a zip fastener canvas was put in place, but this was only found on the prototype Overstrand and was quickly replaced by a simple canvas strip held in place by clips. While the horizontal movement of the turret was done via pneumatic power, elevating the gun was manual. To assist the gunner in this regard, his seat and the gun mount remained balanced with one another and would raise and lower with the gun. Turning the turret was done via applying pressure to plungers on each side of the gun. To prevent the gunner from damaging the aircraft or turret, if rotated with the gun lowered more than 70 degrees to the rear, it would release the pressure from the plunger and stop the turret before the barrel could hit the body. The seat could also be adjusted manually by the gunner. For emergencies, the top dome of the turret could be removed to allow the gunner to exit. The top was held onto the turret via 3 pins, which were locked via pins with finger rings. Removing these three and pushing the top off allowed the gunner to escape. At the rear of the turret was a door that could be opened to enter the airframe of the aircraft. In addition to holding the gunner, the turret also served as the bombardier’s position. The bottom of the turret was heavily glazed to allow downwards visibility. Bomb controls were located to the left of the gun and were also duplicated in the cockpit for the pilot. The bomb sight could not be used in normal use and was stowed away. For bombing, the turret was locked forward into position and the gun moved so the bomb sight could be used.

Front and interior views of the powered turret. (Boulton Paul Aircraft Since 1915)

Aside from the frontal turret, there were two other gunner positions on the aircraft’s rear; one ventral and one dorsal. Both would use the same .303 Lewis gun as the main turret. Many improvements were done over the basic Sidestrand to allow the Overstrand to carry much more weight, including an enlarged bomb load of 1500 Ibs. Two 500 Ibs bombs could be carried internall,y with two additional 250 Ibs bombs on external racks on the fuselage, Additional racks could be installed at the front and rear of the fuselage, each carrying either 4 20 Ibs bombs or 2 20 Ibs bombs and two flares.

The Overstrand Takes Flight

A side view of the completed prototype J9186. This aircraft was converted from a Sidestrand III. (Boulton Paul Aircraft)

The modifications to Sidestrand J1896 would be completed around August of 1933. On its maiden flight, the aircraft would seemingly catch fire, as smoke poured from one of the inner wings. The craft would land immediately, the culprit being found to be caused by fresh varnish on the heating system ducts. Despite this incident happening on the first flight, testing continued on the aircraft. The early days of testing the aircraft yielded two incidents which could be considered quite humorous. After a test flight not long after the first, J1896 would have one of its wheels fall into a hole on the airfield, causing the aircraft to fall forward. One of the propellers would be destroyed and the nose turret would hit the ground. The current occupant of the turret was a member of the armaments section, someone who personally helped with the creation of the turret itself. When the turret dug into the ground, he began to panic and called out for help from the ground crew as he attempted to escape the turret. Due to his panicked state, he had forgotten how to operate the emergency pins that held the top of the turret on. The ground crew found his situation ironic, one of the men who had helped create the turret had forgotten how to operate it in his panicked state. He was in no danger whatsoever and the crew eventually helped the man out. Sometime later, the Air Ministry was intrigued in seeing the progress of the innovative powered turret system and thus sent an official to inspect it. The official was allowed to enter the cockpit to try out the new device. While trying the controls, he accidentally pushed on one of the plungers and began spinning. The gun itself had also been raised over 70 degrees, allowing a full 360 degrees of rotation. In a vain attempt to stop, the official leaned against the gun, and unknowingly onto the plunger; making the turret spin continuously against the intentions of the man. Humored by the situation, the design team that was showcasing the turret simply let him exhaust the air supply and finally let him out once the turret stopped spinning. The Overstrand would make its first debut to the public in late 1933, where it was part of the “Parade and Fly Past of Experimental Types” at the Hendon Air Display. On February 22nd, 1934, the prototype flew to be tested firsthand with the 101 squadron at Andover, who had been operating the Sidestrand up to this point. The main goal was to receive feedback on the changes to the Sidestrand’s design by its would-be operators, if the new additions were at all effective in increasing crew comfort. Aerial tests began and the crews liked the new design for a number of reasons, but they also had their criticisms. Being February, the heating system was very appreciated by the crews. Thanks to its Pegasus engines, the aircraft could attain a top speed of 153 mph (246.2 km/h) while still being as maneuverable as its predecessor. Despite all of this praise, pilots noted that the aircraft felt sluggish on the controls longitudinally and that the engines caused excessive vibrations. Gunners enjoyed not being subjected to harsh winds in the newly enclosed turret, but many felt it was currently too claustrophobic. With the necessary information received, the prototype would leave Andover and return on March 19th. Revisions began immediately to fix the criticisms of the design. A second Sidestrand was converted into this new design (J9770), and the new revisions were input into the modifications of this aircraft. The turret was widened to give the gunner’s more space. The zip-fastened canvas that protected the open slit of the turret was removed in favor of a simple canvas strip that was held on by strips. To accommodate the widened turret, the fuselage nose was widened to a slight degree. Changes were done to improve the autopilot, elevators, and fins to fix the vibration issues. The two-bladed propellers of the Sidestrand were replaced with four-bladed metal ones. Work was also done to make it easier to work on the engine’s compressors. The engines were replaced by the newer Pegasus II.M3 to increase performance and all would be equipped with this engine after this point. By this point in development, the aircraft design would receive a new official name, the Overstrand, named after a town near the city of Sidestrand, the namesake of its base design. Work began on converting two more Sidestrands (J9179 and J9185) into Overstrands not long after the second was completed. Further testing of the types revealed that the aircraft was still having issues with engine vibration. This would plague the converted Sidestrands but was noticeably more tame on the later production versions.

A side view of J9770. This was the 2nd converted Sidestrand and would evenutally be equipped with Pegasus IV engines. (https://www . destinationsjourney . com/)

While Boulton & Paul was in the midst of developing their new bomber, financial issues finally caught up to the company. With the failure to procure production contracts on several aircraft in the past and the Sidestrand itself not performing as well as had previously hoped, Boulton & Paul made the decision that of their four divisions of the company, the Aircraft Division had been the weakest. The Aircraft Division was completely sold off to a financial group, Electric and General Industries Trust Ltd, who would reformat the division into its own dedicated company that would be simply named Boulton Paul Ltd. Despite this drastic change happening with the development team, Boulton Paul would continue their work on the Overstrand starting on June 30th, 1934.

With the early success of the converted Sidestrands, the RAF put out an order (Specification 23/24) to Boulton Paul, which requisitioned the production of 19 newly-built Overstrands to begin replacing the Sidestrands in service.

In Service

A production Overstrand with a Sidestrand in the background. (Boulton Paul Aircraft Since 1915)

On January 24th, 1935, the very first Overstrand would enter service with the 101st Squadron. The squadron itself was already quite familiar with the design, thanks to the testing done the year before, as well as an Overstrand being flown by No.101 squadron members at the 1934 Hendon Air Display. Here, the Overstrand would participate in a mock dogfight against 3 Bristol Bulldog fighters (This display and the rest of the air show can be viewed at the Imperial War Museum’s website, found here.). The plan was to introduce the Overstrand slowly into the squadron, at first forming a third C flight and eventually replacing the Sidestrands in A and B flights. In late May, the Overstrands participated in a bombing demonstration to officials and students of the Imperial Defense College. The target was 200 yards by 300 yards and was meant to represent a bridge. All three bombing runs hit the target and impressed the students with their accuracy. Many however were not so impressed, as the demonstration did not represent accurate combat conditions the bombers would face in battle against a target that would no doubt be defended. Further showcasing of the new bomber continued as on July 6th, No.101 would fly to Mildenhall for the King’s Jubilee Air Review. While there, King George VI would personally inspect Overstrand J9185, and he was particularly interested in the powered turret.

With the necessary modifications made to the designs from actual criticisms of the prototype, the Overstrand and its many accommodations made the aircraft very well liked by the crews who flew them. The Overstrand was a comfortable aircraft to be in, but was also a well performing aircraft no less. At the start of its service, bomb aiming accuracy went up from only 15% accuracy to 85% thanks to the well thought out turret design which factored in bomb-aiming equipment. On top of bomb-aiming, the No.101 Squadron won the Sassoon Trophy of 1935 for photo-reconnaissance with a score of 89.5% accuracy. Gunner accuracy is also noted as having improved considerably thanks to the turret design.

Starting in September, newly produced Overstrands would begin entering service with the No.101 squadron. The first accident with an Overstrand occurred on September 9th, when J9185 crashed at the North Coates Range. Despite this accident, newly built Overstrands would continue to enter service through January of 1936. Before the year would close, an order for five more Overstrands (K8173-K8177) was placed, to serve as replacements in the event any were lost. This would bring aircraft production up to a total of 28 aircraft. While most of the Overstrands would be delivered to the No.101 squadron, K4552 would be sent to the Air Armament School at East-Church, where it would serve as a training aircraft for recruits to become familiar with the type and turret. 1936 was a largely uneventful year for the Sidestrand aside from 3 separate accidents. J9197 would lose an engine shortly after takeoff, K4556 would be forced down in a bog and K4562 would have its brakes seize up on landing.

The aftermath of the crash of K4556. (Boulton Paul Aircraft)

In January of 1937, the RAF began expanding its forces, and creating new squadrons. The No.144 Squadron was formed in support of No.101 and would borrow four Overstrands until new aircraft were made available. The Overstrands would serve for only a month until new Bristol Blenheim bombers could be supplied, after which the Overstrands were returned. Also in January, K4564 would crash while flying in thick fog from Midenhall to Bicester. Unfortunately, the aircraft would be destroyed and the crew was killed. Another aircraft would crash in June. A notice was put out to modify all Overstrands by reinforcing the nose to reduce vibration. Overstrands would once again appear at the Hendon Air Display, however, this would be the last year it was held. An Overstrand would perform a mid-air refuel with a Vickers Viriginia and yet again a mock dog fight would be held, this time an Overstrand would go against three Hawker Demon fighters.

The modified nose of K1785 with the de Buysson turret. (Boulton Paul Defiant: A Technical Guide)

In 1935, Boulton Paul purchased the rights to build the de Buysson electric turret from the Societe d’Applications des Machines Motrices (SAMM) in France. De Buysson was an engineer in the organization and had designed a four-gun electrically powered turret for use on aircraft. The French government was not interested in pursuing it, but de Buysson had caught wind of Boulton Paul’s work on turrets with the Overstrand. SAMM approached the company with their turret design and John North, lead aircraft designer at Boulton Paul, found their turret design superior and purchased the rights to its patent. In 1937, Overstrand K8175, one of the reserve aircraft, was experimentally modified with a de Buysson turret. The turret heavily increased the firepower of the Overstrand from a single Lewis gun to four Barne guns in the nose. Despite the increase in firepower, K8175 would be the only Overstrand to be equipped with this turret. The de Buysson turret would serve as the basis for the turret used in the developing P.82 turret fighter, which would be soon to be renamed the Defiant. Another Overstrand, K8176, would have its turret heavily modified to house a 20mm Hispano cannon. The nose of this aircraft had to be changed drastically to equip this weapon, and the turret was now built into the fuselage. The weapon itself was now on a mount that rotated and most of the glazing of the nose was removed, while what was necessary for bomb-aiming remained.

The modified nose of K1786 with its 20mm Hispano cannon. (Boulton Paul Aircraft Since 1915)

The P.80 Superstrand: A Bomber Behind the Times

Aside from the various modifications done to the Overstrand, there are two known variants that were proposed:

Early in development, Boulton Paul pitched an idea of a variant of an Overstrand that would be converted for coastal reconnaissance, designated P.77. While this idea was pitched, it was found to be largely unnecessary, as the Avro Anson could easily fill this role, and it was a modern monoplane design.

The P.80 Superstrand was meant to be the final evolution of the design, using Pegasus IV engines, retractable landing gear and a redesigned cockpit. While expected performance was much better than the Overstrand, the design was already outdated as it was being made, as newer and more advanced monoplane bombers were entering production, the need for further refining the type was made unnecessary. (Boulton Paul Aircraft Since 1915)

At some point during its service, the second Overstrand built (J9770) was re-equipped with much stronger Pegasus IV engines to increase performance of the aircraft. Plans were further done to modernize the design with retractable landing gear. The development continued with further refinements to the design, eventually becoming a new design entirely. The P.80 Superstrand was meant to be the final step in the bomber’s design, incorporating many modern aspects that were not found on the Overstrand. Aside from the previously mentioned Pegasus IV engines and retractable landing gear, the aircraft would also use variable-pitch propellers. The cockpit section was also redesigned, now connecting the pilot’s position with the rear dorsal gunner’s. The dorsal gunner position was also now fully enclosed. The front turret had many changes done to the design as well. Only the upper section of the turret would now be transparent, and it appears that the front section was now part of the fuselage, with accommodations in the nose for a bomb sight. It was expected these changes to the Overstrand would increase the top speed to 191 mph (307 km/h), give it a maximum ceiling of 27,500 ft and an increase bomb load. The Superstrand was never built, as the aircraft was obsolete even as it was being designed. While the Overstrand was performing well, aircraft development had continued and was now pushing towards more modern monoplane aircraft designs, the opposite of what the Superstrand was. Even Boulton Paul itself, by this point, was beginning to design monoplane bombers. The previous numeric design, the P.79, was a monoplane twin-engine bomber that, while never built, incorporated many elements found in the Overstrand but now adapted onto a more modern airframe. No further work was done on bringing the P.80 to reality.

End of the Line

Direct front view of an Overstrand. (Boulton Paul Aircraft Since 1915)

By 1938, the Overstrand was beginning to show its age. Modern bombers, like the Bristol Blenheim and even larger aircraft, such as the Vickers Wellington, had already, or were soon to enter production and replace the biplanes that remained in service. The Overstrand was no exception. On August 27th, No.101 squadron began gradually replacing their Overstrand bombers with Blenheims. By summer of next year, the Overstrand would be completely removed from frontline service. Despite this, the aircraft still continued to fly in various training schools and serve auxiliary roles. 5 Overstrands were sent to the No.2 Air Observer School in 1938 for training. K4552 would be sent to the No.1 Air Observer school in Lincolnshire, where it would continue its training mission until it was deemed non-airworthy and repurposed to a ground instructional frame. Despite not being in the air, the airframe was still the victim of accidents and, on April 28th, 1940, would be damaged and scrapped after a Gloster Gauntlet trainer overshot and hit it. The final nail in the coffin for most Overstrands came in July, when K1873 would break up mid air, killing the crew. After this incident, all Overstrands were ordered to remain in training as ground instructional air frames only.

K8175 parked in front of the aircraft hangar at the Boulton Paul factory at Wolverhampton. (Boulton Paul Aircraft Since 1915)

Despite this order, a handful of Overstrands would continue flying as part of rather unorthodox missions. K8176 would be sent to be used by the Special Duty Flight at Christchurch. Eventually, this aircraft would be sent to the Army Cooperation Development unit. K4559 would be operated by the Balloon Development Unit at Cardington. There, the aircraft would provide a slipstream for barrage balloons and would test the fatigue of the cables to the balloons. By 1941, the aircraft type was deemed obsolete and it is believed the previously mentioned aircraft were returned to Boulton Paul for turret development. Not long after, K1876 would be involved in an accident due to bad weather. While flying to Edinburgh, the aircraft would attempt to land at Blackpool but would undershoot the runway and crash. This is known to be the last time an Overstrand flew. It is interesting to note that K1876 had just been painted with camouflage, which would make it possibly the only Overstrand that was not in the standard bare metal finish aside from the prototype. It is unlikely any Overstrands saw any combat by happenstance during their short period of operation in the Second World War.

With the type obsolete, all remaining Overstrands were scrapped. While no surviving aircraft remain to this day, a reproduction of the nose section of Overstrand K4556 was built and currently resides in the Norfolk and Suffolk Aviation Museum, in the Boulton Paul Hangar.

Conclusion

The reproduction of the nose of an Overstrand at the Norfolk and Suffolk Aviation Musuem. (https://www . aviationmuseum . net/index . html)

Ultimately, the reason the Boulton Paul Overstrand existed was to improve the pre-existing Sidestrand’s nose gunner position and create a faster platform, which it would successfully accomplish with its reworks. The Overstrand served for only a few years before more advanced aircraft would replace it, but in that time it became a well respected aircraft that was liked by its crews for the various comforts incorporated into the design and which increased the performance.

The Overstrand was a very interesting aircraft, as it seems to be in an area between eras. On one hand, it represents the last of the biplane bombers that can trace their lineage back to the First World War for Britain and for Boulton & Paul. But on the other hand, it had features that were soon to become commonplace. The powered turret design was a game-changer not only for British aviation, but the company that built it as well. Boulton Paul, under H.A.Hughes, would become one of the most prolific turret designers for British aviation in the Second World War, not only designing turrets for use on other bombers, but also with their own upcoming turret fighter design, the Defiant.

Variants

Sidestrand Mk V -The name given to the design at the start of its development.
Prototype Overstrand (J9186) – The very first Overstrand was a converted Sidestrand. This had a smaller turret, two-bladed propellers and a narrower nose.
Converted Sidestrands (J9770, J9179, J9185)– The next three Overstrands built were modified from existing Sidestrands. However, these would be further improved over the prototype by having their turrets widened, four-bladed propellers installed and a wider nose to accommodate the bigger turret.
Boulton Paul P.75 Overstrand – Production version. 24 built in total.
Boulton Paul P.77 – Variant of the Overstrand redesigned for coastal reconnaissance. None were built.
Boulton Paul P.80 Superstrand – The final design of the “Strand” family, the P.80 Superstrand was drawn up in the mid 1930s as to further refine the Overtrand’s design with more modern components, including retractable landing gear, Pegasus IV engines, a reworked turret, lengthened cockpit and further streamlined airframe. Due to monoplane bombers now becoming mainstream, the P.80 was seen as obsolete and none of the type were built.

Modifications

Overstrand K8175 – Production Overstrand that was experimentally modified to test the du Boysson 4-gun turret.
Overstrand K8176 – Production Overstrand that was experimentally modified to house a 20 mm Hispano cannon in its nose turret via pedestal mount.
Overstrand J9770 – The second converted Sidestrand, this aircraft was later experimentally modified to house Pegasus IV engines. This was done as part of the development that would lead to the P.80 Superstrand.

Operators

United Kingdom – The Royal Air Force would operate the Boulton Paul Overstrand from 1935 to 1941 in various squadrons. Most of these would fly operationally with the 101 squadron from 1935 to 1938. The type would also briefly serve with 114 squadron for only a month, until it would be replaced by Blenheim bombers. During WWII, the remaining Overstrands would be relegated to training duties and other special tasks, such as working with barrage balloons.