Sinclair ZX Spectrum cass. published 39 years ago by Software Projects

Listed and emulated in MAME.

Ometron © 1983 Software Projects

Stuck out on a lonely uninhabited outpost of the empire, your mission is to protect the landing site from the hostile forces. You are in a prime site, right in the middle of the landing grid, armed to the teeth with cannons in a revolving turret. Nothing is going to get past you...or is it?