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U3  VETERANS CREW   

Submerging

To make the submarine submerge, you must balance its weight and buoyancy. A settled procedure is utilized for calculating weight differences from a standard condition to establish the actual mass of the boat. That includes stores, crew number, torpedoes, tank contents etc. The amount of compensating water required to be taken into the compensating tank is thus settled. Fore and aft balance is settled by pumping water between trim tanks. The boat is now in trim to submerge.

Submarine U3 Diving controls for flooding and venting of ballast tanks.
U3 Diving controls for flooding and venting of ballast tanks. Photo U3 archives.

The submerging starts by flooding the ballast tanks. Flooding and vent valves in each tank are opened. Flooding took approx 20 sec and the procedure to get the boat submerged lasted 30 sec. If all preparations were correct, the boat would now be in trim submerged. It is now easy to control the boat by means of the control surfaces and propulsion. Smaller deviations in fore and aft trim and weight deviations is now easily adjusted trough operating the trim and weight compensating systems.

Submarine U3 diving. Air is escaping from forward main ballast tanks.
U3 diving. Air is escaping from forward main ballast tanks. Photo U3 archives.

When the submarine was to regain surfaced position, ballast tanks vent valves were checked closed, flood valves opened and high pressure (HP) air was let into the main ballast tanks to empty them. To save H P air, after the initial blowing, it could be followed by letting exhausts from the running diesel engines to enter the ballast tanks.

Submarine Equipment for steering and depth control, 1 helms man 1 planes man.
Equipment for steering and depth control, 1 helms man 1 planes man. Photo U3 archives.