Maritime patrol refers to active patrol of an area, as opposed to passive monitoring systems such as sound-detection fixtures or land-based spotters. A patrol consists of a ship, submarine, aircraft or satellite examining the patrolled area and seeking out activities to be identified and reported. Maritime patrol is critical in wartime situations for navies to locate enemy forces to engage or defend against. Peacetime patrols are important for interdiction of criminal activities and for ensuring legal use of waters.
Maritime patrols can be conducted by surface ships and submarines, by aircraft (e.g. MPA) and other aerial vehicles, and even by satellites. Human spotting remains an important part of detecting activity, but increasingly electronic systems are used.