To shore up its need for a dedicated night fighter in 1940, the United States Army Air Corps (USAAC) went ahead with modified Douglas A-20 "Havoc" / "Boston" light bombers to suit the role. Development began in 1942 in anticipation that the series would not have to fight for long as the Northrop P-61 "Black Widow" - purposely designed for night fighting - would soon arrive in 1943. As such, 163 conversions were made and these across a few notable marks - some never to see combat exposure at all. An XP-70 served as the series prototype to prove the validity of the conversion and the aircraft then operated under the formal designation of P-70 "Nighthawk". All P-70s were delivered before September of 1942.
It was the British Royal Air Force (RAF) that first realized the A-20 as a night fighter when they converted their A-20 Havocs for the role by installing appropriate air intercept radar and a ventral gun pod. The naturally-glazed nose section was painted over/hard-covered to shroud the radar suite and an additional internal fuel tank was fitted for extended operational ranges. The USAAC followed suit, arming their A-20s and outfitting them with local copies of the British AI Mk IV radar (as the SCR-540). These aircraft too lost their glazed nose sections. Some fitted a ventral cannon tray with 4 x 20mm cannons while others utilized a "gun nose" mounting 6 or 8 x 0.50 M2 Browning heavy machine guns - continuing the American reliance on all-machine-gun armament for their aircraft. 2 x 0.50 machine guns were fitted under the nose to fire tracer rounds, useful in gun-laying. In these forms, the radar suite was moved to the bomb bay. The armor protection encountered in the original A-20 was reduced to help lighten the operation loads of the P-70s. It was deemed that such an aircraft, in its given role, need not burden itself down with unnecessary protection.
The Douglas A-20 airframe proved a solid choice for the mission ahead. Its dual-engine configuration, particularly over expansive oceans, meant that the aircraft could fly on a single engine if forced. The multiple crew spread the workload around helping to reduce pilot fatigue. Cannon armament - or similar forward-firing firepower - was a prerequisite considering that the crew would have, at best, a single drive against an enemy target and best make the first shots count.
P-70 marked original base Nighthawks numbering 59 examples. The P-70A-1 mark emerged from the A-20C production model and totaled 39 examples while the 65 P-70A-2s came from the A-20G. The P-70B-1 was the A-20G-10-DO night fighter conversion (single example) and P-70B-2s were A-20G and A-20J models reserved for training future P-61 crews - these aircraft outfitted with SCR-720 and SCR-729 radar kits.
In practice, the P-70 proved a serviceable machine but was only ever fielded in the Pacific Theater. There was already a converted A-20 with radar on station over California after the Japanese attack at Pearl to prove the aircraft-radar combination sound. First deliveries of P-70s was in April of 1942 with machine gun noses while retaining support for 2,000lb of internal stores if needed. The A-1s then followed in 1943 during a period when night fighters were in constant need against marauding Japanese raiders. While P-70s lacked much in the way of flat-out speed and high-altitude work (they lacked superchargers), they provided a solution where there initial proved none to be found. its usefulness was limited with the arrival of the dedicated P-61 in 1944 and other converted types which promised better results and performance. By the start of 1945, all P-70s were removed from frontline service, thus ending their operational tenures in World War 2, and served as trainers until their final days. Indeed, the P-70 trainers graduated some 485 persons to serve in American night fighter squadrons.