While working at this company, Northrop focused on the
flying wing design, which he was convinced was the next major step in aircraft design. His first project, a reduced-scale version tested in 1940, ultimately became the giant
Northrop XB-35. The
Northrop XP-56 Black Bullet, a welded magnesium fighter was one of the more significant of his World War II designs, along with the
Northrop P-61 Black Widow, the first American night interceptor, of which more than 700 were constructed. His inventions continued into the postwar era of jet aircraft, to produce the
Northrop F-89 Scorpion all-weather interceptor, the
Northrop YB-49 long-range bomber, the
Northrop Snark intercontinental missile, and automatic celestial navigation systems. He produced a number of flying wings, including the
Northrop N-1M,
Northrop N-9M, and
Northrop XB-35. His ideas regarding flying wing technology were years ahead of the computer and electronic advances of "fly-by-wire" stability systems which allow inherently unstable aircraft like the
B-2 Spirit flying wing to be flown like a conventional aircraft. The flying wing and the pursuit of low drag high lift designs were Northrop's passion and its failure to be selected as the next generation bomber platform after World War II, and the subsequent dismantling of all prototypes and incomplete YB-49s, were a severe blow to him. He retired at age 57 in 1952 and virtually ended his association with the company for the next 30 years. ==Later years==