I found an interesting article concerning US torpedoes. Below is a link to that article. The article recaps the different torpedoes and discusses all the problems that plagued the early commanders in the Pacific (1941 to late 1943). Of particular note I found two keys items:
1. The TDC device was designed for the Mark 14 and later model torpedoes and the TDC was only fitted in Fleet boats (the S class was too small for a TDC).
2. S boats only carried Mark 10 torpedoes (this type only used a contact exploder).
http://www.fleetsubmarine.com/torpedoes.html
So, perhaps when playing Silent Hunter 4 in a early campaign a person may have a easier time engaging and sinking the enemy by using the old S boats (using the old Mark 10 torpedo with a contact exploder), instead of a Fleet boat that has the TDC and defective Mark 14 torpedoes.