Loss of Bouyancy
 

The easy way to increase bouyancy is to blow air into the tanks. This could be done in an emergency but would take surface time to replace the compressed air.

You don't pump water at depth you displace it with air. It's noisy and agiveaway to surface DD Sonar operators. Without the air to displace the volume of water removed the tank would crush like a can...

We gave them some things in exchange ofr the magnetron and other secrets, that included the torpedoe trigger. Being we found them defective and in need of repair does not surprise me that the British Sub fleet did the same. Lend Lease also transfered a number of S Boats tothe the Brits and the Poles along with their Warloads....

WWII Submarine Doctrine Official Policy
 

This is an excerpt from WWII Submarine Doctrine manual

1. Enemy target propeller turn counts are taken whenever possible and are of valuable assistance in estimating target speeds. These should never be used conclusively and must not be used to supplant plotting or other methods of determining target speed for use in solving the torpedo problem. Changes of speed are readily detected by propeller count.
   
2. Echo ranging during the conduct of an approach must be used with discretion and with full consideration of many factors. If it is certain that enemy craft lack the equipment necessary to detect transmission from own equipment on the frequencies used, it can then be used with impunity. Under these conditions, when approaching an unscreened target, echo ranging can no doubt be used effectively for checking course and speed, for solution of the torpedo problem, and for own maneuvers in conducting the final stages of the approach. The importance of obtaining a single ping range at about 2500-3000 yards in order to accurately determine target masthead height with which to correct speed data is obvious. Under these same conditions, periscope observations are usually available, but when the masthead height of the target has to be estimated, echo ranges may be more accurate than periscope ranges. If the target is surrounded by a screen, the problem of ranges through wakes left by screens will be difficult. The results must be evaluated before they are used conclusively if a valuable target has made herself subject to attack.

:know:

You still have to set ship speed at 10 knots, as you and your torp will also be subject to the current, unless of course the ship is in a very narrow 'current channel' - If you're aware of this channel you'll be lucky.
:)

This is funny coz from '43 onwards, when this book is based, the brit torpedoes were still dodgey. This may have been due to faulty production methods more than technology, but still the same result.:)

O'Kane talks about poor torpedo performance experienced on one of the patrols of the Tang. I don't remember the date. It was so bad, they decided to pull into a quiet inlet, in Japan, at night, so they could observe their runs. An anchored gunboat was there, so they used it for a target. They had to fire 3 or 4 shots to hit it, though it didn't move. IIRC, he blamed manufacturing defects; said torpedo components were made by subcontractors, who had little understanding of what they were making or its function.

The popular conception is of torpedo designs being flawed at the start, and then at a certain date being "fixed", but I think the reality was more complicated. This should not be too big a surprise; torpedos were the most complex pieces of ordnance in their day, comparable to todays "smart weapons".