F-16 Fighting Falcon

Genesis of the successful F-16 fighter/attack aircraft lies in reaction to severe deficiencies in US fighter design revealed by the Vietnam War.

Following the success of the small, highly maneuverable F-86 day fighter in the Korean War, US fighter design changed to emphasize maximum speed, altitude, and radar capability at the expense of maneuverability, pilot vision, and other attributes needed for close combat. This trend reached its extremity in the McDonnell Douglas F-4 Phantom, which was the principal fighter for both the US Air Force and Navy during the latter part of the Vietnam War.

The F-4 was originally designed as an interceptor for defense of the fleet against air attack - a mission neither it nor any other jet has ever executed, because no US fleet has come under air attack since the beginning of the jet age. Be that as it may, the F-4 interceptor was designed to meet the fleet defense mission by using rapid climb to high altitude, high supersonic speed, and radar-guided missiles to shoot down threat aircraft at long distance.

Used as a fighter rather than as an interceptor in Vietnam, the F-4 was severely miscast. Against very inferior North Vietnamese pilots flying small, highly maneuverable MiG-21s, the air-to-air kill ratio sometimes dropped as low as 2 to 1, where it had been 13 to 1 in Korea. As the Vietnam War drew to a close, it was generally agreed that the F-4 had prohibitive deficiencies including:

1. LARGENESS. F-4 pilots to frequently found themselves fighting at separation distances at which they could not see the smaller MiG-21s, but the MiG-21 pilots could see them.
2. POOR PILOT VISION. In order to minimize high-speed drag, the F-4, and all combat aircraft before the F-14, does not have a bubble canopy. It is designed for a pilot to look straight ahead. Vision down and to the sides is poor; vision to the rear is nonexistent.
3. MANEUVERABILITY. While the F-4 can pull 7G in turns, which was acceptable for that time, it can only do so by rapidly bleeding off energy (losing speed and/or altitude).
4. TRANSIENT PERFORMANCE. Ability of the F-4 to change its maneuver (that is, to roll rapidly while pulling high Gs) was poor.
5. COST. The large F-4 was an expensive aircraft to procure and maintain. This meant that, compared to the MiG-21, fewer aircraft could be bought with a given budget.
6. NO GUN. The F-4 was designed without a gun, and was thus not capable of very close combat.
7. COMBAT PERSISTENCE. While the ferry range of the F-4 was acceptable, its ability to engage in sustained hard maneuvering without running out of fuel was a significant problem.

Source: fas.org and other website