USS Harder, Sam Dealey, heard scuttlebutt that the Japanese were running short of escorts and made it a point to sink destroyers whenever possible.

http://www.history.navy.mil/danfs/h2/harder-i.htm

Not necessarily a "suicide mission", after all as soon as you sink a merchant in a convoy with 4 escorts you have 4 escorts hunting for you to rain depth charges on your head. Sink one of the destroyers instead now you have 3 escorts instead of 4 since the one you sank won't be bothering you anymore. What I often do is dive deep to find out where the layer is, then attack a destroyer with two fish, down the throat with three at the next one, then go to flank speed, kick out a decoy and dive below the layer before slowing down. Sink all the escorts first and you can surface to clobber all the unprotected merchant ships with the deck gun, wipe out the entire convoy.

:arrgh!:

I've seen this before too. I've pretty much run some version of tmo since I quit stock.