Design and development
Handley Page produced the H.P.56 design to meet Air Ministry Specification P.13/36 for a twin-engine medium bomber for “world-wide use”. Other candidates for the specification were the Avro Manchester and a Vickers Warwick development; all used twin Rolls-Royce Vulture engines. The introduction of the successful P.13/36 candidates were delayed by the necessity of ordering more Armstrong-Whitworth Whitley and Vickers Wellington bombers first.
 Performance and reliabilty with the under-developed Vulture was found to be lacking. Modifications resulted in the definitive H.P.57 which upon acceptance gained the name “Halifax” following the practice of naming heavy bombers after major towns; in this case Halifax in the West Riding of Yorkshire. The H.P.57 was enlarged and powered by four 1,280 hp (950 kW) Rolls-Royce Merlin X engines. Such was the promise of the new model that the RAF had placed their first order for 100 Mk I Halifaxes “off the drawing board” before the first prototype even flew. The maiden flight of the Halifax took place on 24 September 1939 from RAF Bicester, 21 days after the UK declared war on Germany.  The Halifax production subsequently began at English Electric’s site at Samlesbury, Lancashire with over 2,000 bombers being built at the factory during the war.  The Mk I had a 22 ft long bomb bay as well as six bomb cells in the wings, enabling it to carry 13,000 lb (5,897 kg) of bombs. Defensive armament consisted of two .303-in Browning machine guns in a Boulton Paul Type C nose turret, and four in BP Type E tail turret and, in some aircraft, two Vickers K guns in beam positions. The Merlins drove constant speed wooden screw Rotol propellers. Subtle modifications distinguished the Mk I aircraft. The first batch (of 50) Mk I Halifaxes were designated Mk I Series I. The Halifax Mk I series had a serious flaw in the design of its tail units that caused it to go into a steep, uncontrollable spin if the aeroplane lost engine power from two engines on the same wing[1] or it was flung about vigorously. This fault undoubtedly caused a number of fatal crashes.  These were followed by 25 of the Mk I Series II with increased gross weight (from 58,000 lb (26,000 kg) to 60,000 lb) but with maximum landing weight unchanged at 50,000 lb (23,000 kg). The Mk I Series III had increased fuel capacity (1,882 gallons), and larger oil coolers to accept the Merlin XX. A two-gun BP Type C turret mounted dorsally replaced the beam guns.  Introduction of 1,390 hp (1,040 kW) Merlin XX engines and a twin .303-in dorsal turret instead of waist guns resulted in the B Mk II Series I Halifax. The Mk II Series I (Special) achieved improved performance by removing the nose and dorsal turrets. The Mk II Series IA had a moulded Perspex nose (the standard for future Halifax variants), a four-gun Defiant-type dorsal turret, Merlin 22 engines and larger vertical tail surfaces which solved control deficiencies (rudder-stall) in the early Marks. Halifax IIs were built by English Electric and Handley Page; 200 and 100 aircraft respectively.  Due to a shortage in Messier-built landing gear and hydraulics Dowty landing gear were used. Being incompatible with the Messier equipment these gave Halifaxes with new designations. A Mark II built with Dowty gear was the Mark V. The use of castings rather than forgings in the Dowty undercarriage speeded production but resulted in a reduced landing weight of 40,000 lb (18,000 kg). The Mark V were built by Rootes Group at Speke and Fairey at Stockport and were generally used by Coastal Command and for training. Some 904 were built by the time Mark V production ended at the start of 1944 compared to 1,966 Mk II.  The most numerous Halifax variant was the B Mk III of which 2,091 were built. First appearing in 1943, the Mk III featured the Perspex nose and modified tail of the Mk II Series IA but replaced the Merlin with the more powerful 1,650 hp (1,230 kW) Bristol Hercules XVI radial engine. Other changes included de Havilland Hydromatic propellers and rounded wing tips. The Mk IV was a non-production design using a turbocharged Hercules powerplant.  The definitive version of the Halifax was the B Mk VI, powered by the 1,800 hp (1,300 kW) Hercules 100. The final bomber version, the Mk VII, reverted to the less powerful Hercules XVI. However, these variants were produced in relatively small quantities.  The remaining variants were the C Mk VIII unarmed transport (8,000 lb cargo pannier instead of a bomb bay, space for 11 passengers) and the Mk A IX paratroop transport (space for 16 paratroopers and gear). A transport/cargo version of the Halifax was also produced, known as the Handley Page Halton.  Total Halifaxproduction was 6,176 with the last aircraft delivered in November 1946. In addition to Handley Page, Halifaxes were built by English Electric, Fairey Aviation, Rootes Motors (Rootes Securities Ltd.) and the London Aircraft Production Group. Peak production resulted in one Halifax being completed every hour. Courtesy Wikipedia  |
