Boulton Paul P.29 Sidestrand & P.75 Overstrand

boulton paul sidestrand overstrand

While perhaps occupying a less prestigious place in history than Supermarine or Avro, Boulton Paul Aircraft Ltd nevertheless helped forge British military aviation. The company’s name, Boulton Paul, has a rich heritage as ironmongers stretching as far back as 1797. Prospering in the Industrial Revolution of Victorian Britain the firm evolved to become a general manufacturer by the start of the 20th century before founding an engineering division in 1905. It would be this engineering division that would lay the foundation for Boulton Paul Aircraft Ltd and this was thanks to the outbreak of World War I.

Despite a somewhat muddled start aircraft were now proving indispensable over the Western Front and the Royal Flying Corps was going through a rapid expansion. In order to meet the demand for its F.E.2b combat aircraft the Royal Aircraft Factory approached Boulton Paul to manufacture 550 airframes and thus Boulton Paul became an aircraft manufacturer albeit building other company’s products. During the course of the war a number of companies sub-contracted Boulton Paul to build their designs and this gave the company’s engineers a wealth of experience to the extent that the company then decided to attempt to design and manufacture aircraft themselves.

P.3 Bobolink (

P.3 Bobolink (

To help them in this bold endeavour in 1917 they brought in John Dudley North an established engineer who had worked on aircraft designs for the Austin Motor Company. The fruits of this new department could be seen in the company’s first aircraft the P.3 Bobolink, a prototype for a new fighter to replace the Sopwith Camel which the company had intimate knowledge of thanks to a sub-contract to build it from Sopwith. This knowledge was obvious in Boulton Paul’s aircraft as in many ways it resembled the previous Sopwith design. Boulton Paul’s aircraft was rejected in favour of the Sopwith Snipe and it would be only the first of a series of promising but ultimately disappointing attempts to design and build their own aircraft for the newly established Royal Air Force.

With the end of the war Boulton Paul Aircraft Ltd needed to establish itself quickly in the British aviation scene if it was to survive and that was no easy feat. Several of the main manufacturers of aircraft during the war collapsed within two years of the armistice the biggest shock being Sopwith who’s Camel and Snipe had been credited with winning back air superiority over the Western Front. In 1918 the RAF was already looking for a new bomber to replace its wartime Handley Page O-series aircraft and Boulton Paul saw this as an opportunity to show that it was capable of competing with the best.

John Dudley North began work on the P.7 Bourges to meet the RAF’s specification. North adopted the tried and tested design of a large biplane design with a gunner/bomb aimer in the exposed nose of the aircraft and the pilot seated behind. Despite good flying qualities the aircraft was ultimately never acquired by the RAF and after four years of redesigns in an effort to entice interest in the aircraft it was finally dropped in 1924 when the RAF rescinded and revised the original requirement. North tried to redesign the aircraft in to a transatlantic airliner but this failed also.

Boulton Paul P.7 Bourges (

Boulton Paul P.7 Bourges (

North and Boulton Paul Aircraft Ltd remained undeterred however and produced a series of one-off prototypes building on the Bourges. While none of these were successful the company was continuing to gain experience and Boulton Paul as a whole was getting enough work to keep North’s division open. The company’s efforts had not gone entirely unnoticed however and other companies began to view Boulton Paul as a serious competitor for contracts. Finally in 1924 the Air Ministry issued a specification for a three/four seat medium day bomber to replace their wartime fleet of aircraft. North took all he had learned from his previous prototypes and put that knowledge in to a single design which was given the in-house designation P.29.

The P.29 had an overall similar configuration to his previous designs stretching back to the Bourges but was more bloated in appearance as North designed the aircraft with sweeping lines for increased aerodynamic efficiency. The aircraft was of mixed metal and traditional wood/canvas construction with thin steel skin covering the main frame around the cockpit. Identifying the vulnerability of the wartime bombers to enemy fighters the P.29 was designed to be heavily armed for its day with three gunner positions in total – one in the nose, one behind the pilot and one in the lower half of the fuselage facing backwards. Each gunner was armed with a single manually trainable .303 (7.7mm) Lewis machine gun while the aircraft was designed to carry an offensive load of 1,000lbs of bombs.

Boulton Paul Sidestrand I (

Boulton Paul Sidestrand (

Power for the aircraft was to come from a pair of Bristol Jupiter VIIF 9-cylinder air-cooled radial engines. These were geared to produce 460hp each and were mounted in streamlined nacelles on the lower wing. Originally North wanted to power the aircraft with Napier Lion inline engines and the shape of the nacelles retained a look more akin to an inline engine at the rear. The Jupiter was a sound alternative choice by North as the engine was a well-established and proven powerplant. Many aircraft designers in the 1920s remembered the “Dragonfly debacle” – the decision by the Air Ministry in 1918 to standardize the RAF’s aircraft on the ABC Dragonfly engine. The engine was so problematic and repeatedly delayed that many advanced aircraft projects stalled and were then cancelled as a result such as the Avro 533 Manchester bomber and Sopwith’s last fighter design the Snark.

The Air Ministry was suitably impressed with the design on paper to authorise the construction of two prototypes for flight testing in early 1925 with the first prototype, J7938, being completed in March the following year. It fell down to Boulton Paul’s first full-time test pilot, Flight Lieutenant Cecil Arthur Rea, to take the aircraft aloft for the first time. After initial flight testing was completed the company handed the aircraft over to the RAF for service trials at Martlesham Heath. A second prototype, J7939, was under construction at the same time and would be demonstrated at the 1927 Hendon air display under the rather clinical name of “Hendon Display New Type No. 8.” Testing at Martlesham Heath with J7938 revealed that the bomber had quite lively performance for an aircraft of its size but in a time before power assisted controls throwing it around the sky was a laborious affair leaving the pilot quite exhausted if done for extended periods. The RAF pilots also complained that the aircraft suffered from quite severe vibration when running the engines at high power. This was seen as of little importance however since it was not expected to be flown like a fighter and so the RAF turned their interest in to an acquisition. After showing so much promise John North and Boulton Paul finally got one of their aircraft in to frontline service.

The name “Sidestrand” was chosen by the Secretary of State for Air in 1927, Samuel Hoare, in honour of his home town of Sidestrand, Norfolk. The two prototypes therefore became known as Sidestrand Mk.Is but some minor redesign was requested by the RAF to help alleviate the vibration problems following the trials at Martlesham Heath. This resulted in the Sidestrand II the first six of which were powered by the same Jupiter VIIF engines as the prototype before production switched to the Jupiter VIIIF after six airframes were completed. The Jupiter VIIIF equipped versions subsequently adopted the designation Sidestrand III and all six Mk.IIs were upgraded to this standard.

Sidestrand III Specifications

Role: Medium Day Bomber
Maximum speed: 139mph
Range: 520 miles (approx operational range)
Powerplant: 2x Bristol Jupiter VIIIF 9-cylinder air-cooled radial engine (460hp each)
Service ceiling: 20,800ft
Length: 46ft 0in
Wingspan: 71ft 11in
Height: 14ft 9in
Defensive Armament: 3x .303in (7.7 mm) Lewis guns (nose, dorsal and ventral positions)
Offensive Armament: 1,040lbs of bombs

Boulton Paul Sidestrand (

Boulton Paul Sidestrand (

After full service acceptance No.101 Squadron was selected as the first Sidestrand unit replacing their increasingly ageing De Havilland DH.9As. However the RAF’s interest in the type was suddenly waning as it became clear that despite it being a new design it offered performance that was little better than some of the twin engine bombers it was expected to replace and with new types like the Fairey Hendon monoplane under development it was clear the Sidestrand was obsolete technology. In the end only twenty aircraft would be built and No.101 Squadron would be the only frontline unit to equip with the type.

All was not lost for Boulton Paul however. They did at least have their foot in the RAF’s door with an aircraft that sported their logo and realising their concerns they began work on a further improved version in 1932. The Jupiter VIIIFs were dropped in place of far more powerful Bristol Pegasus II.M3 9-cylinder radial engines which each churned out 580hp.

Boulton Paul Overstrand gun turret (

Boulton Paul Overstrand gun turret (

This increased the aircraft’s speed but this in turn presented another problem as a result of the open cockpit and gun positions. For the forward gunner aiming the .303 Lewis gun was extremely difficult thanks to the increased headwind while the pilot found his face being blasted with air throughout the flight. At about the same time Boulton Paul was experimenting in developing powered gun turrets and they decided to put this in to practice by scabbing a powered gun turret on to the nose of the Sidestrand. It was heavily glazed and offered a greater forward field of vision to the gunner who at the same time felt a little more vulnerable even though he was no safer in the older model. The turret was rotated by pneumatic motors while elevation and depression of the single Lewis gun was achieved by hydraulic rams. The cockpit was also given a glazed canopy and the new Sidestrand Mk.V was considered so different to its predecessor that the RAF decided to rename the aircraft as the Overstrand after another village in Norfolk.

First flying in 1933 the Overstrand could fly faster, higher and carry a heavier bomb load than the Sidestrand III. The first examples were converted from Sidestrand IIIs before production examples entered service again with the RAF’s No.101 Squadron to replace the earlier machines in 1934 (the last Sidestrand IIIs were retired in 1936). Nevertheless despite these advances it was clear that the new aircraft was only a stop gap until the newer monoplanes became ready. An Overstrand II was proposed with a retractable undercarriage and this later became known as the Superstrand but it never left John North’s drawing board. Only 28 Overstrands were eventually built including the original conversions and they served with No.101 Squadron until 1938 when they were replaced by Bristol Blenheims. A number of Overstrands were operated by the newly reformed No.144 Squadron in 1937 to keep the pilots current until a number of Avro Ansons arrived allowing them to return the aircraft to No.101 Squadron.

Boulton Paul Overstrand (commons.wikimedia)

Boulton Paul Overstrand (commons.wikimedia)

After No.101 Squadron relinquished their Overstrands in 1938 the aircraft were divided up amongst gunnery training schools. A number of aircraft also served with the RAF’s Balloon Development Unit designing new barrage balloons. The RAF had little interest in keeping their aircraft in service for any extended period of time and so effectively worked them all to death. In 1941 the last aircraft was withdrawn from a gunnery training school.

Although the Overstrand’s career could be considered unspectacular it does hold two accolades to its name. It was the aircraft that introduced the powered turret to regular RAF service and the experience both the RAF and Boulton Paul gained from it went in to developing more powerful and successful gun turret/aircraft combinations. It was also the last biplane bomber to serve in the RAF thus closing the opening chapter of Bomber Command’s technical history. Only two Overstrands were ever lost in accidents both of which proved fatal but percentage-wise this was a small figure compared to other types then in service.

Boulton Paul Aircraft Ltd would never make a massive impression on British aviation like Avro, Hawker or Supermarine but they did have one final “ace” to produce before they ended their efforts to build their own aircraft. The Boulton Paul Defiant combined their expertise in building aircraft with their growing expertise in gun turret technology. Early success with the RAF over France was overshadowed by a sudden rise in losses as Luftwaffe pilots developed tactics to counter the aircraft. Nevertheless the Defiant helped form an effective early part of the RAF’s nightfighter force and it was thanks largely to the story of Boulton Paul’s forgotten bombers.

Overstrand I Specifications

Crew: 4
Role: Medium Day Bomber
Maximum speed: 148mph
Range: 545 miles (approx operational range)
Powerplant: 2 × Bristol Pegasus II.M3 9 cylinder radial engine (580hp each)
Service ceiling: 21,300ft
Length: 46ft 0in
Wingspan: 72ft 0in
Height: 15ft 6in
Defensive Armament: 3x .303in (7.7 mm) Lewis guns (nose, dorsal and ventral positions)
Offensive Armament: 1,500lbs of bombs


11 responses to “Boulton Paul P.29 Sidestrand & P.75 Overstrand

  1. Pingback: Defence of the Realm – Royal Air Force | Defence of the Realm

  2. Very informative.

    At first I was not much interested with that topic, but since this article was from you, I was sure to learn something…which I did.

    Thanks for posting.

    Liked by 1 person

  3. Bolton Paul were always the poor mans aircraft maker, or so it seemed, yet they managed to produce some interesting aircraft that helped shape the future of aircraft and in particular, bomber design. Another interesting post Tony.

    Liked by 1 person

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