CAP is also an acronym for Combat Air Patrol, the practice of maintaining interceptor aircraft aloft with the intent of preventing incursions on a specified area. U.S. Carrier battle groups maintain a CAP at nearly all times. In the aftermath of the NY/DC bombings on 9/11/01, it has been reported by noders that there are F-16s and other types from the USAF flying CAP over New York City and Washington, D.C. to prevent any aircraft from approaching.

Related term: BARCAP, for BARrier CAP. This means a set of CAP missions/units whose purpose is to prevent other aircraft from crossing a designated 'line' or 'barrier' as opposed to responding to incursions into an area.