Combat air patrol (CAP) is a type of defensive mission for fighter aircraft, in which they guard a designated site, either a fixed site on land, ships at sea, or less commonly support aircraft such as aerial tankers .

It typically entails fighters flying some sort of pattern around the defended object, while looking for incoming attackers. Effective CAP patterns may include aircraft positioned at both high and low altitudes, so as to shorten response times when the attack is detected.

CAP is especially characteristic of aircraft carrier operations, where the CAP is flow to protect the carrier battle group. There are also BARCAP and TARCAP missions:

• A BARrier Combat Air Patrol (BARCAP) is flown between the CVBG and the direction from which it is most likely that enemy attack will come.
• A TARget Combat Air Patrol (TARCAP) is flown over or near a strike target in order to protect specialised attack aircraft from harassment by enemy fighters.

The real-life activity inspired the computer game Combat Air Patrol, a flight simulator published by Psygnosis in 1995.

Reference

Griffith, Paddy (1991). The Ultimate Weaponry. Sidgwick & Jackson.