Prairie/Masker is a radiated noise reduction system fitted to some warships of western origin, including the DD-963 and DDG-51-class destroyers and the CG-47-class cruisers. The Masker portion consists of two bands fitted to the outside of the hull adjacent the vessel's engine rooms, compressed air is then forced into the bands and escapes through machined perforations to create a barrier of air bubbles in the sea about the hull, thus trapping machinery noise. Prairie works via the same principles but is fitted either near to or on the ships propellors. The systems are designed to prevent classification/identification by radiated noise of the warship in question by acoustical analysis, i.e. by a hostile submarine. Instead of hearing machinery, the ship sounds similar to rain on passive son