How deep could the submarine be and still fire a torpedo?

We know that the boat was supposed to be deeper than 150 feet when using the Mark 27 homing torpedo. There was a safety mechanism to protect the boat if it was at that depth. However, that was for a defensive weapon. Most attacks required visual bearings and ranges. The boat would be on the surface or at periscope depth for the attack. That meant it was rarely deeper than about 63 feet.

Early in the war, captains were told to fire on sonar bearings. That wasn’t accurate enough and was discontinued. However, at that time the deepest firings were likely no deeper than 100 to 150 feet.