The Jill of the Jungle game reminded me of another very old game. Probably from the DOS days. I have tried searching the internet archives site and others like that.

Some of this description might be wrong due to faulty memories.
The game was on a riverboat/gunboat. It was a vertical scrolling game. You traveled up the river while shooting at enemies on the riverbank. You manned a machine gun mounted at the middle of the boat. Probably double barrel. I 'think' it was in isometric view. It could have been an Atari 800 game.

Any ideas? I have this silly 'ear-worm' in my head about this.

Is it gunboat?
[url=]https://en.wikipedia.org/wiki/Gunboat_(video_game)[/url]

YES! Thank you. Now I feel like a total tool. I did google for a bunch of different names but I must have missed 'gunboat'. Crud.

If you like that game I would also recommend Stellar 7 and its sequel if you can get them.