A submarine-launched missile (SM) is a guided missile fired from a submarine. Some SMs are placed in launch capsules to be fired through the submarine's torpedo tubes. These missiles are initially solid-propellant motor-driven, and once clear of the water (and launch capsule) ignite their booster motor. An exception is the future IDAS missile of the German Navy, which will be tube-launched, but is fired directly from the torpedo tubes without emerging in a capsule.