Abstract: A plurality of similarly constructed gas generators are disposed in the ballast tanks of a submarine vehicle, each generator decomposing hydrazine in an emergency gase for developing a particular amount of gas for blowing all or a part of a ballast tank. Each gas generator has a hydrazine reactor, one or two storage containers for hydrazine and either a pump for moving hydrazine to the reactor; or a container filled with driving gas for the same purpose; or both. The number of gas generators triggered depends on the depth of the craft in each instance, and once a generator has been triggered, the development of gas by the generator does not depend on any control, but a triggered generator develops all of the gas it is capable of developing.