A fourth-generation jet fighter optimized for Cold War defense of U.S. Navy Carrier Strike Groups, but enjoying a long service life in which it gained fighter-bomber and reconnaissance capabilities. Originally, it was intended for the "outer air battle": intercepting Soviet bombers carrying long-range anti-shipping missiles, beyond the range at which they could launch: over 250mi/400 km from the high value asset ships in the center of the task force.
To do this, the aircraft was designed around a missile with unprecedentedly long range, the AIM-54 Phoenix, and a matching long-range radar, the AN/AWG-9. Since the primary targets were relatively unmaneuverable bombers, and the secondary targets large cruise missiles that they launched, the Phoenix did not need complex terminal guidance, but needed high speed to get the long range. The aircraft could simultaneously track 24 targets and guide 6 missiles.
It replaced the F-4 Phantom II in Navy use; the F-4 also was extensively used by U.S. Air Force. U.S. Secretary of Defense Robert McNamara ordered a common replacement for the F-4, with variants for Air Force and Navy requirements, called the Tactical Fighter Experimental (TFX) program. The TFX became the F-111, which was never able to meet Navy requirements, and, while adopted by the Air Force, it was as a bomber, not a tactical fighter.
When the services split their developments, the Air Force built the F-15 Eagle. Both services found that their best fighters, the F-14 and F-15, were extremely expensive. John Boyd conceived of a "high-low" mix, which the Air Force adopted before the Navy. The Air Force complemented the F-15 with the F-16 Fighting Falcon; only considerably later would the Navy commit to the F-18 Hornet.
Surprisingly for a fighter, the Tomcat was among the heaviest aircraft ever to operate from an aircraft carrier. The "A" version had underpowered engines, and could not land on the carrier with a full load of missiles; it would have to jettison expensive ordnance or take off with a smaller load.
Due to its large size, but need to operate from carriers, it had variable-geometry wings, which could be spread wide for slow carrier landing but folded to a delta for high supersonic performance. While the wings worked well, they were mechanically complex, and different aerodynamic control methods are used in more modern aircraft.