Northrop YP-61 from below
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The Northrop P-61 Black Widow was the only American-built purpose build night fighter to enter service during the Second World War, and was one of the largest and most sophisticated fighter aircraft of its era. Perhaps as a result of this the development of the P-61 was slow, and although work began late in 1940 it didn't enter service until 1944.
The Black Widow was born in the London Blitz. Both Jack Northrop and General Delos Emmons (Commander, HQ, Army Air Corps) saw some of the night bombing at first hand. During a visit to London to discuss the Vultee Vengeance the British outlined their requirements for a night fighter to Northrop. This called for an aircraft with the ability to stay airborne for up to eight hours, fast enough to catch the German bombers, and armed with gun turrets (to leave the pilot free to concentrate on intercepting the elusive bombers). The slow development of the Black Widow meant that it never actually saw service with the RAF, being beaten into service by the Bristol Beaufighter and by nightfighter versions of the de Havilland Mosquito.
On his return from London General Emmons came to the conclusion that the Army Air Corps needed its own night interceptor. In the autumn of 1940 the Emmons board drew up a preliminary specification, and on 21 October 1940 this was presented to Vladimir Pavlecka, Northrop's Chief of Research.
Pavlecka and Northrop compared notes, and came to the conclusion that the large twin engined aircraft Northrop had been planning for the British would also satisfy the American specification. With this head start Northrop only needed a week to produce a proposal, and they were able to present their ideas to the Air Corps on 5 November 1940. After some further design work, on 17 December 1940 Northrop were given a Letter of Authority to produce two prototypes and two small scale models, with the designation XP-61 (the formal contract followed on 10 January 1941). This was followed by a contract for thirteen service-test aircraft (YP-61s) and one static test bed, issued on 10 March 1941.
The original Northrop design was for a twin engined, twin boomed aircraft, armed with nose and tail turrets. The turrets were then moved to upper and lower positions, before the lower turret was replaced by wing mounted guns, and after the inspection of the first mock-up by four 20mm cannon mounted in the central fuselage. The upper turret was retained, although it was removed from most early production aircraft, and when it was installed was often fixed in place to increase the forward firepower. Given that the turret also caused development and production delays, its inclusion was probably a mistake.
The first XP-61 made its official maiden flight on 26 May 1942, having left the ground during a high speed taxi test five days earlier (the first production contract, for 150 aircraft, was placed on 1 September 1941, nine months before the maiden flight). While the prototype had been developed creditably quickly, it would be another two years before the aircraft entered service. After a promising first flight, later tests revealed problems with the 'Zap' flap – a full-span retractable flap used in place of more conventional controls, and this had to be replaced with small ailerons and normal flaps. The YP-61s were not completed until August-September 1943, and the first production P-61A was finished in October 1943.
The P-61 entered service during 1944. It made a relatively minor contribution to the war effort, arriving too late and in too limited numbers to be really influential. Despite these limits the P-61 was a technical success, with the speed, stability and firepower needed to make it a first class night fighter. Its arrival was a particular relief in the Pacific, where the small number of night-fighter squadrons had been struggling with unsuitable aircraft.
