Google is your friend.
http://en.wikipedia.org/wiki/Mark_18_torpedo
The Mk 18 was based on the German G7e. They wanted a wakeless electric torpedo. They accepted that there would be problems, but the wakeless torpedo was needed. Apparently it was popular because the potential problems were unknown and the benefits were believed at the time to outweigh any negatives.
http://www.hnsa.org/doc/torpedomk18/index.htm