Handley Page Halifax - Design and Development

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 included the Avro 679, and designs from Fairey, Boulton Paul and Shorts; all used twin engines – Rolls-Royce Vultures, Napier Sabres, the Fairey P.24 or Bristol Hercules. A four-engined wing was then still a new idea in British bombers. The introduction of the successful P.13/36 candidates was delayed by the necessity of ordering more Armstrong-Whitworth Whitley and Vickers Wellington bombers first.

The Avro and HP.56 designs were ordered "off the drawing board" in mid 1937, with the Avro design as the preferred choice. Soon after Handley Page was told to redesign the HP.56 for four engines rather than two, as the Vulture was already suffering technical problems. The Avro Manchester would be built with Vultures but suffered due to them. This redesign increased the span from 88 feet (27 m) to 99 feet (30 m) and put 13,000 pounds (5,900 kg) of weight on. 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, just 21 days after the UK declared war on Germany.

The Halifax production subsequently began at Handley Page's (now English Electric) site in Samlesbury, Lancashire, with over 2,000 bombers being built by this factory during the war.

The Mk.I had a 22 ft (6.7 m) long bomb bay as well as six bomb cells in the wings, enabling it to carry 13,000 lb (5,900 kg) of bombs. Defensive armament consisted of two .303 in (7.7 mm) Browning machine guns in a Boulton Paul Type C nose turret, with an additional four in a Boulton Paul Type E tail turret, and, in some aircraft, two .303 in (7.7 mm) Vickers K machine guns in beam (side, or "waist") 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.

These were followed by 25 of the Mk I Series II with increased gross weight (from 58,000 lb/26,310 kg to 60,000 lb/27,220 kg) but with maximum landing weight unchanged at 50,000 lb (23,000 kg). The Mk I Series III had increased fuel capacity (1,882 gal/8,556 L), 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 (7.7 mm) 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, trapezoidal-shaped vertical tail surfaces which solved control deficiencies from fin-stall with the roughly triangular-shape original surfaces, leading to rudder overbalance) 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 was used. Being incompatible with the Messier equipment this 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/3,630 kg 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.

The bomb aimer's position was in the extreme nose with the navigator's table behind it; the posts being fulfilled by the same crew member. Separated by a half width partition the wireless (radio) operator was behind the navigator's partition. Above the navigator was the forward gun turret and the pilot and co-pilot above the wireless operator. Aft of the pilots was the flight engineer's compartment. A further compartment aft of the flight engineer led to the dorsal turret.