A personal flotation device (abbreviated as PFD; also referred to as, lifejacket, life preserver, Mae West, life vest, life saver, cork jacket, buoyancy aid, flotation suit, etc.) is a device designed to assist a wearer, either conscious or unconscious, to keep afloat. Devices designed and approved by authorities for use by civilians (recreational boaters, sailors, canoeists, kayakers, etc.) differ from those designed for use by passengers and crew of aircraft (helicopters, airplanes) and of commercial vessels (tugs, passenger ferries, cargo ships). Devices used by military (army, air force, special forces, marines, navy, coast guard) and police and enforcement agencies generally have features not found on civilian or commercial models, for example compatibility with other worn kit (e.g. survival vest, bulletproof vest/body armor, equipment harness, rappelling harness, parachute). PFDs are available in different sizes and different designs purposed for various levels of protection.