H.P.52 Hampden Mk.I
With the Japanese invasion of Manchuria in 1932 and the collapse of the Geneva disarmament conference, the RAF finally came to the realisation that their biplane bombers were inadequate, and the new generation of monoplane bombers like the H.P.47 had inadequate payload or range for operations into Europe, so a specification was prepared for an advance twin-engined, monoplane, retractable landing gear bomber.
HP learned of this specification early, and Lachmann worked to design an aircraft at the cutting edge of 1932 technology. The aircraft was an ultra-narrow fuselage development of the aerodynamics of the H.P.47, extending the design principles that worked on reducing the size and hence weight and drag of the rear fuselage boom and tailplane structure. The design was still capped to a maximum size due to the bomber restrictions of the League of Nations. An initial prototype was commissioned, and before construction Imperial Airways requested a civil version to compete against the German civil Ju.86. Due to secrecy, HP was not permitted to work on this tender, however another tender from Sweden was permitted and became the H.P.53.
The initial H.P.52 prototype battled through designs for turrets, and was eventually flown with simple glazing in preparation for the design of definitive turrets, including an extended tail for a remote gun barbette. The prototype first flew in June 1936, and was displayed at the RAF display at Hendon shortly after, and in August production of 180 aircraft was ordered.
Final production dropped the tail barbette and the nose turret, however used in the H.P.54 Harrow, while the narrow fuselage also meant that no dorsal turrets could be easily mounted and so the Westland-style gunner's canopy planned for the H.P.47 was adopted. To improve handling the wing dihedral was also increased.
The first production H.P.52 finally flew on 21 June 1938, and was officially christened on the 24th.
Rapid production of the H.P.52 led to 770 aircraft being built by March 1942, supplied to both the RAF and Commonwealth forces. The aircraft were initially used in both the day and night bomber roles, but by the time that war had started they were already outdated and outgunned by German fighters, and after significant loses were withdrawn from daylight bombing.
With their later withdrawal from night bomber duties as well, some H.P.52's were allocated to Coastal Command and modified for meteorological reporting duties to become H.P.52 Met.I aircraft.
Another role the H.P.52 was adapted to was as a torpedo bomber. The standard British Mk.XII torpedo
almost fitted within the bomb bay, so a minimal modification at the rear gunner's position was required, and the bomb bay doors were required to be left slightly open to allow the carriage of the torpedo. The torpedo itself required the fitment of an auxiliary rear fin to allow the required (relatively) high speed and height for dropping without causing torpedo instability. This structure was considered secret, so most photos of the time have been censored to remove sight of the fin. Additionally as the bomb bay was otherwise committed, the aircraft were fitted with underwing bomb racks.
The H.P.52 was obsolete by the time the Phoney War was over, but it was a type that bought Britain breathing space to design a bomber force able to fight in the 1940's.