It was part of the trio of large twin-engine bombers procured for the RAF, joining the Armstrong Whitworth Whitley and Vickers Wellington.

The Hampden was powered by Bristol Pegasus radial engines but a variant known as the Handley Page Hereford had in-line Napier Daggers.

The Handley Page design team, led by George Volkert, drafted a radical aircraft, initially centering upon the politically favoured Rolls-Royce Goshawk engine.

According to aviation author Philip J.R. Moyes, the Handley Page design soon found support with the Air Ministry in part because it was judged to represent a fair compromise between range, payload, and speed.

On seeing the narrow-yet-deep fuselage, which was only 3 ft wide, C. G. Grey, founder of The Aeroplane magazine, remarked "it looks like a flying suitcase", a nickname that stuck with the aircraft for its lifetime.

[4] L4032 differed from the previous two prototypes in that it was powered by a pair of Pegasus XVIII engines, the nose incorporated an optically flat bomb-aiming panel, as well as the ventral and dorsal gun positions being revised.

[4] On 24 June 1938, L4032 was officially christened by Lady Katharine Mary Montagu-Douglas-Scott, Viscountess Hampden, at a ceremony held in Radlett Aerodrome, the same day on which its first flight took place.

[7] On 20 September 1938, the third production Hampden, designated L4034, following the completion of handling trials conducted by the Central Flying School at Upavon Aerodrome, Wiltshire, become the first aircraft to enter RAF squadron service, being delivered to No.

Designated P.5 by the RSAF, it was operated by the service until November 1945, after which it was sold to Svenska Aeroplan AB (SAAB) to serve as a flying testbed before being retired in late 1947.

Conceived as a fast, manoeuvrable "fighting bomber", the Hampden had a fixed forward-firing .303 in (7.7 mm) Browning machine gun in the upper part of the fuselage nose.

[12] According to Moyes, the configuration of the wing was a key feature of Hampden, being highly tapered and designed to exert low levels of drag; these attributes were responsible for the aircraft's high top speed for the era of 265 mph (230 kn; 426 km/h) while retaining a reasonably low landing speed of 73 mph (63 kn; 117 km/h).

[14] Upon introduction, the Hampden exhibited greater speeds and initial climb rates than any of its contemporaries while still retaining favourable handling qualities.

[18] A total of 226 Hampdens were in service with ten squadrons by the start of the Second World War, with six forming the operational strength of 5 Group of Bomber Command based in Lincolnshire.

[18][19] With the outbreak of war in 1939, Hampdens were initially used to perform armed aerial reconnaissance missions, observing German naval activity during daylight.

[20] On 13 April 1940, days after Germany's invasion of Norway, a large number of Hampdens were dispatched on night-time mine-laying (code-named "gardening") flights in the North Sea in areas deemed unapproachable by British shipping.

[11] On 19 March 1940, Hampdens took part in the first deliberate bombing of German soil in a nighttime raid upon the seaplane hangars and slipways in Hörnum, Sylt.

Flight Lieutenant Rod Learoyd of 49 Squadron was awarded the Victoria Cross for a low-level attack on the Dortmund-Ems canal on 12 August 1940 where two of five aircraft failed to return.

[23] Sergeant John Hannah was the wireless operator/air gunner of an 83 Squadron Hampden and was awarded the Victoria Cross on 15 September 1940, when he fought the flames of the burning aircraft, allowing the pilot to return it to base.

Typical exercises at 32 OTU consisted of patrolling up the West Coast of Vancouver Island at night or flying out into the Pacific to a navigational map co-ordinate, often in adverse and un-forecast inclement weather.

455 Squadron RAAF flew to Northwest Russia, to protect arctic convoy PQ 18 from German surface vessels, such the battleship Tirpitz.

This was a hazardous route, often subject to poor weather and spanning more than 2,100 nautical miles (3,900 km), partly over enemy-occupied territory in Norway and Finland.

Aircrews and mechanics from Maritime Military Fleet Aviation (Aviatsiya Voenno-Morskogo Flota; VMF) were trained by members of 144 and 455 Squadrons, before their return to Britain in October.

[31] The 3rd Squadron, 24th Mine-Torpedo Aviation Regiment (24 Минно-торпедный авиаполк; 24 MTAP) operated the "balalaika" – the Russian nickname for the Hampden, in reference to its unusual shape – until mid-1943,[32] when losses, a lack of replacements and a shortage of spares forced its retirement.

A Mk II variant, designated the HP.62, was developed by converting two Hampdens to use the 1,000 hp (750 kW) Wright Cyclone engine in 1940, but no further work was done on that project.

[23] Interest in the HP.52 by the Swedish Air Force led to the creation of the HP.53 prototype, which was subsequently used as a testbed for a pair of 1,000 hp (750 kW) Napier Dagger VIII 24-cylinder H-block air-cooled inline engines.