The Handley Page Halifax is a British Royal Air Force (RAF) four-engined heavy bomber of the Second World War.

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."

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.

Various improved versions of the Halifax were introduced, incorporating more powerful engines, a revised defensive turret layout and increased payload.

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.

Power limitations were so serious that the British invested heavily in the development of huge engines in the 2,000 hp (1,500 kW) class to improve performance.

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.

[4] 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.

[6] In February 1937, following consideration of the designs, the Air Ministry selected Avro's submission, with Handley Page's bid chosen as "second string".

[8] Further design modifications resulted in the definitive aircraft, now considerably enlarged and powered by four 1,280 hp (950 kW) Rolls-Royce Merlin X engines.

In order to speed up production, Handley Page implemented several new manufacturing techniques, including two pioneering approaches: photo-lofting and split construction.

[16] 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 Halifax B Mk.II Series I.

The Halifax Mark V were manufactured by Rootes Group at Speke and Fairey at Stockport; operationally, these were generally used by Coastal Command and for training purposes.

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.

[23] The Handley Page Halifax was a mostly orthodox design, a mid-wing monoplane with a tail unit featuring twin fins and rudders.

[4] Each engine drove a Rotol-built compressed wood constant-speed propeller, enabling the Halifax B.I to attain a maximum speed of 265 mph (426 km/h) at 17,500 ft (5,300 m).

Its operational debut occurred on the night of 10–11 March 1941, when six Halifax bombers flew a bombing raid against Le Havre, targeting the area around the docks and any shipping that might be present.

At the end of 1941, the Halifax was withdrawn from daylight bombing operations after intensifying fighter opposition had increased the casualty rates to unsustainable levels.

[10] While the early-built models of the Halifax were heavily used by Bomber Command and made valuable contributions to operations, the aircraft's performance was considered unsatisfactory for the most part, mainly due to the underpowered Merlin engine, which meant that it could not fly at the higher altitudes needed to avoid enemy fighters, which were becoming increasingly effective throughout 1943.

We much appreciate your telegram of congratulation on Saturday night's work, the success of which was very largely due to your support in giving us such a powerful weapon to wield.

"[32] Following the invasion of Europe in 1944, the Halifax resumed daylight bombing operations, performing semi-tactical strikes upon enemy troop concentrations, gun emplacements, and strongpoints of the Atlantic Wall defences along the French coast with a reportedly high degree of accuracy.

[33] The Halifax also found itself being increasingly tasked with transport duties around this time; in one instance, around half a million gallons of petrol was delivered to Brussels in support of the advancing Second Army, then engaged in heavy fighting at Arnhem.

578 Squadron for displaying great gallantry in bringing his heavily damaged aircraft back after a raid on Nuremberg on the night of 30/31 March 1944.

[37] Throughout early 1945, the Halifax was frequently dispatched against cities within the German homeland, including Hannover, Magdeburg, Stuttgart, Cologne, Münster, Osnabrück and others.

According to Moyes, within the final few months, bomber losses had fallen to all-time lows while raids were frequently regarded as having been highly successful.

[35] While some of these Mk.VI and Mk.VII machines were deployed to the theatre, they played little meaningful role as the war ended before larger numbers could be brought to bear against Japanese forces.

[38] On 25 April 1945, the Halifax performed its last major operation against the enemy in WWII during an attack upon coastal gun batteries on Wangerooge in the Frisian Islands of the North Sea.

RPAF Halifaxes flew several sorties in support of Pakistani and Kashmiri forces (notably in the Battle of Skardu) during which they conducted night-time Airdrop missions.

Halifax NA337 was recovered in 1995 from 750 ft (230 m) under Lake Mjøsa, Norway before being restored at the National Air Force Museum of Canada in Trenton, Ontario.