The Northrop YF-17 (nicknamed "Cobra") was a prototype lightweight fighter aircraft designed for the United States Air Force's Lightweight Fighter (LWF) technology evaluation program. The LWF was initiated because many in the fighter community believed that aircraft like the F-15 Eagle were too large and expensive for many combat roles. The YF-17 was the culmination of a long line of Northrop designs, beginning with the N-102 Fang in 1956, continuing through the F-5 family.