no need to blow tanks?

[Sailor Steve]

Originally Posted by codmander

...down 200 meters or so the tanks are filled with water and should have to be blown to rise thoughts?:hmm:

When you perform a crash (emergency) dive the tanks are full, and must be partially blown to achieve neutral bouyancy. In a normal dive, and when operating submerged, the tanks are only half (or so) full. Rising and sinking are controlled with the dive planes; this includes surfacing. Either when surfacing or shortly after the tanks are emptied, giving positive bouyancy. If done just before surfacing, this does require compressed air. If done after breaking surface, engine-powered blowers are used.
http://www.maritime.org/fleetsub/chap18.htm#18C

When the torpedoes are fired, some compressed air is used, but compensating for the lost weight of the torpedoes requires taking on water, not expelling it. Here is the straight dope:
http://www.maritime.org/fleetsub/chap19.htm#19A