The Handley Page Halifax is a British Royal Air Force (RAF) four-engined heavy bomber of the Second World War. It was developed by Handley Page to the same specification as the contemporary twin-engine Avro Manchester.

The Halifax has its origins in the twin-engine H.P.56 proposal of the late 1930s, produced in response to the British Air Ministry's Specification P.13/36 for a capable medium bomber for "world-wide use." The H.P.56 was ordered as a backup to the Avro 679, both aircraft being designed to use the Rolls-Royce Vulture engine. The Handley Page design was altered to use four Rolls-Royce Merlin engines while the rival Avro 679 was produced as the twin-engine Avro Manchester which, while regarded as unsuccessful mainly due to the Vulture engine, was a direct predecessor of the Avro Lancaster. Both the Lancaster and the Halifax emerged as capable four-engine strategic bombers, thousands of which were used during the War.

The Halifax performed its first flight on 25 October 1939, and entered service with the RAF on 13 November 1940. It quickly became a major component of Bomber Command, performing strategic bombing missions against the Axis powers, primarily at night. Arthur Harris, the Air Officer Commanding-in-Chief of Bomber Command, described the Halifax as inferior to the rival Lancaster (in part due to its smaller payload) though this opinion was not shared by many of the crews that flew it. Nevertheless, production of the Halifax continued until April 1945. During their service with Bomber Command, AIR 22/203 Bomber Command War manual figures, Halifax flew 73,312 bomber, 3,716 sea mine, 365 anti submarine and 5,745 other sorties (like radio counter measures), total 83,138 sorties, 1,833 aircraft missing, 403 written off, bombs dropped on bombing sorties 224,207 or 223,654.7 long tons, bombs were dropped on other sorties.  Pathfinder Halifax reportedly dropping 474.7 long tons of bombs.

The Halifax was also flown in large numbers by other Allied and Commonwealth nations, such as the Royal Canadian Air Force (RCAF), Royal Australian Air Force (RAAF), and Free French Air Force.

Various improved versions of the Halifax were introduced, incorporating more powerful engines, a revised defensive turret layout and increased payload. It remained in service with Bomber Command until the end of the war, performing a variety of duties in addition to bombing. Specialised versions of the Halifax were developed for troop transport and paradrop operations. After the Second World War, the RAF quickly retired the Halifax, the type being succeeded as a strategic bomber by the Avro Lincoln, an advanced derivative of the Lancaster. During the post-war years, the Halifax was operated by the Royal Egyptian Air Force, the French Air Force and the Royal Pakistan Air Force. The type also entered commercial service for a number of years, used mainly as a freighter. A dedicated civil transport variant, the Handley Page Halton, was also developed and entered airline service; 41 civil Halifax freighters were used during the Berlin Airlift. In 1961, the last remaining Halifax bombers were retired from operational use.

Development Origins

In the 1930s, the Royal Air Force (RAF) was primarily interested in twin-engine bombers. These designs put significant demands on engine production and maintenance, both of which were already stretched with the introduction of many new types of aircraft into service. Power limitations were so serious that the British invested heavily in the development of huge engines in the class to improve performance. However, during the late 1930s, none of these engines were ready for production. Meanwhile, the United States, France, Germany and the Soviet Union were developing bombers powered with four engines with favourable results, including excellent range and lifting capacity. Accordingly, in 1936, the RAF decided to investigate the feasibility of a four-engined bomber.

During the mid-1930s, the British Air Ministry released Specification P.13/36, seeking a twin-engine heavy-medium bomber suitable for "world-wide use". Further requirements of the specification included the use of a mid-mounted cantilever monoplane wing and all-metal construction, and encouraged use of the Rolls-Royce Vulture engine then in development. In response, Handley Page produced the twin-engine H.P.56 design to meet Specification P.13/36. Handley Page aircraft designer George Volkert had responsibility for the design.

Other candidates were submitted for the same specification, including the Avro 679, and designs from Fairey, Boulton Paul and Shorts. All submissions used two engines, using the Rolls-Royce Vulture, Napier Sabre, Fairey P.24 or Bristol Hercules engines. All of these engines were under development and while four-engined bomber designs were considered for specification B.12/36 for a heavy bomber, wings mounting two pairs of engines required additional testing at the Royal Aircraft Establishment (RAE). A stronger wing also required additional strengthening of the overall aircraft structure, increasing design weight.

In February 1937, following consideration of the designs, the Air Ministry selected Avro's submission, with Handley Page's bid chosen as "second string". Accordingly, during April 1937, the Air Ministry ordered two prototypes of each design. The introduction of the successful P.13/36 candidates was delayed by orders for Armstrong-Whitworth Whitley and Vickers Wellington bombers. In mid-1937, it was decided to order both the Avro 679 and H.P.56 designs "off the drawing board" in order to speed up delivery timetables.

During July 1937, Handley Page was instructed to redesign the H.P.56 to use four engines. The Vulture had already been suffering reliability and performance problems. The rival Avro 679 proceeded into service as the Avro Manchester powered by a pair of Vulture engines, but was only built in limited quantities after suffering substantially from engine trouble. The four-engine redesign increased its wingspan from to and added of weight. In September 1937, the Ministry specified the use of four Rolls-Royce Merlin engines; according to aviation author Phillip J. R. Moyes, this redesign to four Merlin engines was done "much against the company's wishes".

Towards the end of the year, a full-size mock-up was assessed and production of a pair of H.P.57 prototypes commenced in March 1938. Further design modifications resulted in the definitive aircraft, now considerably enlarged and powered by four Rolls-Royce Merlin X engines. Such was the promise of the new model that, in January 1938, the RAF chose to place their first production order for the type, ordering 100 Mk.I Halifaxes "off the drawing board", at which point the serials which had already been assigned to the H.P.56 were switched to the H.P.57.

Prototypes

The first prototype was built at Handley Page's facility in Cricklewood, London, It was then dismantled and transported by road to RAF Bicester (the nearest non-operational RAF airfield with suitable facilities) for reassembly. The first flight of the first prototype Halifax, serial number L7244, was performed by chief test pilot Jim Cordes with E A 'Ginger' Wright as flight test observer on 25 October 1939. During this flight, the undercarriage was locked down as a safety precaution. On 17 August 1940, the first flight of the second prototype, L7245, now complete with full armament and operational equipment, was made from Radlett Aerodrome. The H.P.57 was given the service name Halifax upon acceptance. This name followed the practice of naming heavy bombers after major towns, which in this case was Halifax in Yorkshire. In September 1941, a production Halifax Mk.I participated in an official naming ceremony of the type, officiated by Lord Halifax and Lady Halifax.

Production

Series production of the Halifax began at Handley Page's factory at Cricklewood and at English Electric's site in Samlesbury, Lancashire. In order to speed up production, Handley Page implemented several new manufacturing techniques, including two pioneering approaches: photo-lofting and split construction. In the latter capacity, each Halifax was built from various sub-assemblies. Surface panels were flush-riveted, although the matt black night bomber camouflage negated its benefit.Flight pp. 400–401.

Handley Page built the assemblies and components at Cricklewood and the aircraft were assembled and flown from Radlett Aerodrome. The first production aircraft flew from Radlett on 11 October 1940.

The sizeable production run envisioned required the involvement of several other companies in addition to Handley Page. The resulting Halifax Group was established to oversee the manufacturing programme, comprising English Electric (who had previously built Handley Page Hampdens), various firms within the London Aircraft Production Group, Fairey Aviation, and Rootes Motors. Because of this scheme, Halifaxes were manufactured at sites across the British isles.

The Halifax was produced in large numbers during the war and over 40%, or 5,129 of the 12,643 heavy bombers produced in Britain between 1940 and 1944 were Halifaxes. In all, 6,167 Halifaxes were built, the last bomber version in April 1945, last cargo in July 1945, last paratroop in November 1946.  Peak production of 218 in March 1944. At the peak, 41 separate factories and dispersed units were involved in production, along with 600 subcontractors and 51,000 employees. The first English Electric-built aircraft was flown from Samlesbury on 15 August 1941, officially produced in September, first from London Aircraft Production in January 1942, first from Rootes in March 1942, first from Fairey in August 1942.

The first production standard Halifax, the Mk.I, had a long bomb bay and six wing bomb cells, and could carry a load. Defensive armament consisted of two Browning machine guns in a Boulton Paul Type C nose turret, with an additional four in a Boulton Paul Type E tail turret. Some aircraft included two additional Vickers K machine guns in beam (side, or "waist") positions. Subtle modifications distinguished the Mk.I aircraft. Aircraft of the first batch of fifty Mk.I Halifaxes were designated Mk.I Series I. 

A = Paratroop/Glider Tug, C = Cargo.  Six Mark I ordered from Handley page were not built, being used as pattern aircraft for the other production lines, 5 mark III ordered from Fairey were not built, being delivered as sets of components.

+FactoriesManufacturerLocationPrototypeIIIIIIA.IIIVVIVIIA.VIIC.VIIIA.IXTotalHandley PageRadlett285608324157120451001451,586English ElectricPreston900900325202,145Fairey AviationStockport3202462169656London Aircraft Production GroupLeavesden450260710Rootes SecuritiesSpeke12250306581201,070Total2851,9702,054309044821612341001456,167

Improvements Handley Page were initially disappointed with the performance of the Halifax which was below their predictions, much of this was because they had under-estimated the aircraft's drag. The Mk.III Halifax had a wider span of and had significantly improved performance. Arguably the Merlin engine did not suit the Halifax as much as the Hercules (fitted from the Mk.III on) which suited the Halifax better both aerodynamically and in power.

The Halifax Mk.I was quickly followed by 25 of the Mk.I Series II; these featured an increased gross weight from to but with maximum landing weight unchanged at . The Halifax Mk.I Series III featured increased fuel capacity ( and larger oil coolers, the latter of which having been adopted in order to accommodate the Merlin XX engine. A dorsally-mounted two-gun Boulton Paul Type C turret replaced the beam guns.

AVIA 46/112 and the pilot notes indicate the increase to 1,882 gallons came in the mark II, along with a dorsal turret and Merlin XX engines.