Finally, the F-16 Fighting Falcon, later nicknamed the "Viper," also entered the Air Force inventory, initially assigned to the 388th Tactical Fighter Wing at Hill AFB, Utah in January 1979. With the cost of acquiring the F-15 continuing to escalate in the early and mid-1970s, the F-16 was the successful design of the USAF Lightweight Fighter (LWF) competition, increasing overall USAF tactical fighter numbers with a multi-mission fighter that could replace those F-4 Phantom IIs not replaced by the F-15 in the air-to-air role and being able to concurrently assumed the F-4's role in air-to-ground / interdiction roles.