Torpedoing a 1/2 sunken T-Class?

[kdv]

Had an encounter with a T-Class sub yesterday, took him out from behind as suggested by deck cannon.

Shallow water, so his stern hits the bottom, bow pointing up, but just under the surface. No credit for the kill. Can't shoot the deck cannon underwater, so I waited (and waited and waited), nothing happened.

I backed up my boat just over 300 meters, and fired a dumb torpedo - missed wildly.

Is there any recourse in this kind of situation? Kind of a shame to not get credit for a skillful shoot-out .