This game is based on one I found in an old book.
There is a submarine in the playfield. When a depth charge is dropped, the size of the explosion will indicate how close to the submarine it exploded.
From time to time, it will move, trying to avoid destruction.
There are a few aids available.
A range finder will give you a more positive distance indication than the size of the explosion.
The direction indicator will tell you which way it is, and the heading indicator, which way it is moving.
The game runs in any CoCo with Extended Color Basic, with a CoCo 3 version coming... sometime.
You can see the source code
, or download a disk image
with it and other programs from the site.