A underwater fight would be close to impossible due to a number of issues
A) The torpedoes were designed to run just below to surface (could be programmed slightly lower)
The targeting of torpedoes was an exercise in trigonometry, and observation of the target (speed course and angle of bow) were needed to calculate the launch. Acoustic torpedoes were used by the germans, but never used in a large scale, and were quite unpredicatble.
C) the amount of compressed air needed to launch a torpedo while submerged lower than a few meters is staggering.
Surface encounters did occurr however, but rather rare.