by expelling liquid ballast

Full Title

Marine torpedoes, e.g. launched by surface vessels or submarines (having additional propulsion means for movement through air F42B17/00); Sea mines having self-propulsion means (F42B12/00 takes precedence; launching means F41F; locating by use of radio or other waves G01S; automatic control of course G05D1/00; firing directors or calculators G06G) > adapted to be used for exercise purposes, e.g. indicating position or course > with means for causing torpedoes to surface at end of run > by expelling liquid ballast