1) 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.


2) Negative Tank - I'll quote directly from the manual:

"Negative tank, located inside MBT 2A and 2B, is used to provide negative buoyancy for a quick dive."

"Negative tank is built to withstand full submergence pressure and can be used as a variable tank..." It's connected to the trim system.

"The snorkel induction mast is drained to the negative tank (when) preparing to snorkel." The same amount of water is blown out of negative at the finish of snorkeling, when the snorkel induction mast refills, with water.


3) 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.


4) Fuel Ballast Tanks - These are nominally ballast tank. But they may be filled with fuel for extended patrols.


5) Collecting and Expansion Tanks - "...collecting tank.....is used as a settling tank to separate oil and water in the compensating system and provide oil for the fuel pump." "The expansion tank.....is used both as an overflow tank when fuel volume expands with temperature and a source of water for the compensating system. It is also used to receive bilge water." (Basic Enlisted Submarine Text)


6) Normal Fuel Oil Tanks - Just what the name says.


7) Main Ballast Tanks - Just what it says.


8) Variable Ballast Tanks - These are part of the trim system and function as follows:

   a) Forward Trim - Used to increase or reduce buoyancy at the bow of the sub.

   b) Forward WRT (Water 'round Torpedoes) - Used to correct for changes in weight (trim)
       when torpedo tubes are loaded or empty, with or without water in them.

   c) Auxiliary Tanks - Used to adjust for changes in ships buoyancy due to
       temperature and salinity changes in the surrounding water.

   d) After WRT - Same as forward WRT, for the stern

   e) After Trim - Same as forward trim, for the stern Water is normally transferred
       between these tanks using the trim pump. But ship's service air may also be used.
       To add or remove water in the trim system it is pumped from or to sea using the
       trim pump. The trim system is also connect to the negative and safety tanks,
       as well as the drain system.

9) Sanitary Tanks - There are three sanitary tank. In the forward torpedo room, after battery and after torpedo room. They are used to store waste water from the heads, showers and sinks in those areas.