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. With the born of the more powerful Airborne Intercept radar, the SCR-720C,the P-61s of the Army began their upgrade to install this latest radar. The new type Black Widow with the SCR-720C were designated as P-61B.The type B length the nose section and reintroduced the dorsal turret on the late production.