 Criticism from the fighter mafia that the F-15 was too large to be a dedicated dogfighter and too expensive to procure in large numbers, led to the Lightweight Fighter (LWF) program, which led to the USAF General Dynamics F-16 Fighting Falcon and the middle-weight Navy McDonnell Douglas F/A-18 Hornet.The single-seat F-15C and two-seat F-15D models entered production in 1978 and conducted their first flights in February and June of that year.These models were fitted with the Production Eagle Package (PEP 2000), which included of additional internal fuel, provisions for exterior conformal fuel tanks, and an increased maximum takeoff weight up to .