Another system gaining popularity is the 'Snort System'. A ballast tank allows water to enter by releasing a vent valve on the top of the cylinder, allowing the boat to submerge. To surface, a small pump 'Snorts' air from the snorkel tube in the conning tower (sail) into the ballast tank, expelling the water. This system is also equipped with a small tank of compressed gas, which in the event of a fail-safe system operating, usually due to loss of radio signal, the gas is released into the ballast tank, surfacing the boat.