Since the Air Force of each country started pay their attention on the night bombing, the bombing became more effective than ever. To fight against the night bombing, a series of night fighter were put into use. The American start their night fighter program on 1940. The Army use the P-70 Havoc and Beaufighter to fight with the Japanese until the first 45 P-61 Black Widow were in active service on October, 1943. The first 37 P-61 were installed with a four gun turret on the back of the fuselage and deleted on the following aircrafts. The first unit to take the P-61A into combat was the 6th Night-Fighter Squadron in Hawaii. The Black Widow soon replace the Douglas P-70s and P-38J on 1 May 1944.