maintaining depth at stop

[Rockin Robbins]

Originally Posted by WEBSTER

IMO all subs made sure they were at some level of negative boyancy any time they werent surfaced

Webster, not to be offensive or anything, but we're not talking about opinion. We are talking about actual practice as verified by the people who actually ran the submarines.

In actual practice there was a tank called the negative buoyancy tank. Once per day the submarine took a "trim dive." Sub jockeys, check my accuracy here and keep me straight. In the trim dive, you dive the sub, slow it way down and with fore and aft trim tanks you level the boat. Somewhat simultaneously you fill or pump negative until the boat is at perfect negative buoyancy. The tank (in WWII anyway) is then marked at the level of neutral buoyancy. Fore and aft trim tanks are calibrated to know how bow or stern heavy the boat is. When a torpedo is fired, ballast equivalent to the weight of the torpedo being fired must be immediately added to the fore or aft trim tank to compensate for the lost weight and still leave the boat in balance.

Part of the diving procedure was to flood negative to the mark. Yes, you remember that, I see. "The mark" would be that neutral buoyancy level established in the trim dive earlier in the day. That way, subject to any changes to conditions since the trim dive, the boat dove adjusted as closely as possible to neutral buoyancy.

Now I will speculate just like you :rotfl:, making an educated guess based on many books I have read by World War II submariners. If a submariner did something that departed from "the book," that would have been remarkable and noted in any of the books I have read. None of them have mentioned flooding negative to a level above the mark.

To me, that means that this part of the procedure was one that maybe was not required, but was one that captains were very reluctant to depart from, just like maintaining under a 10º dive angle, even though after the war the guppies successfully used dive angles that were much greater and speeded dive and surfacing times. Nonetheless, in spite of possible gains from changing the practice, during the war, captains were very precise about adhering to the official guidelines for diving and surfacing procedure.