This game is based on the "Squash Squid" (by R.Stubbs) from Tim Hartnell's 1983 "Giant Book of Spectrum Games". The original BASIC game was 39 lines long (including 3 lines of comments).

In the original, a bomb moved horizontally accross the screen until a key is pressed then it dropped down and (hopefully) collided with a (stationary) squid.
The didn't seem fair to me.

So, in my version a "bomber" moves horizontally, and drops a bomb (when a key is pressed). The hit is scored if the bomb collides with the evil red submarine.
To make this (much) more challenging, I added an option to allow the submarine to (slowly) move.
Enjoy.
S.
PS: I am also posting gemini's translation of the original basic into a free-pascal console app.