Gato Class Ballast System: Bow and Safety Tank by Mike Keating

Bow Buoyancy Tank - Being above the waterline, when surfaced. It has little effect on the Sub's operation. It's only purpose is to give the bow some added buoyancy when surfacing. This reduces the time it takes to surface by bringing the bow up faster than would normally be the case. It is the first tank vented on diving and the first blown on the order to surface.

Safety Tank - Normally, safety tank is kept full of water, and compensation is computed on this basis. In the event of a submerged emergency, it can be blown, giving the boat extra buoyancy. It is, in effect, a margin of safety, hence the name.