 Combat frogmen (Kampfschwimmer) operate offshore undiscovered and in shallow water, but mine clearance divers are used also in lakes and partly into deeper water.The preferred diving equipment of the combat frogmen is accordingly oxygen rebreathers, which reprocesses breathed out air and delivers only small masses of gas to the environment, so that the combat frogman cannot be discovered by rising bubbles.See also German commando frogmen.