The Mark 21 Mod 2 torpedo was a passive acoustic homing variant of the Mark 13 torpedo intended for use as a payload for the AUM-N-2 Petrel guided missile. Development of this torpedo was discontinued and it was not used in service to any extent.
This page contains content from the copyrighted Wikipedia article "Mark 21 Mod 2 torpedo"; that content is used under the GNU Free Documentation License (GFDL). You may redistribute it, verbatim or modified, providing that you comply with the terms of the GFDL.