The hangar is a ship fitting that serves as a launch bay: containers on a heavy frame, plated with steel plate and built in an Assembler. It lets the ship that carries it launch fighters and bombers from its hold in a fight, and take them back aboard once the fight is over. Each hangar adds to the number of craft the ship keeps out at once. The bay takes up room in the hold.
It is a large fitting for a hardpoint, not a slot, so only a warship carries one. It is fitted and removed at a station with a shipyard in the ship's system.