The TDC was unique in World War II. It was the computational part of the first submerged integrated fire control system that could track a target and continuously aim torpedoes by setting their gyro angles. The TDC Mark III gave the U.S. fleet submarine the ability to fire torpedoes without first estimating a future firing position, changing the ship's course, or steering to that position. Instead of hoping that nothing in the setup changed, a fleet submarine with the TDC could fire at the target when the captain judged the probability of making hits to be optimal.

From an article by Terry Lindell