Sentinel is the sequel to "Dimension X", which was released on the Atari 8-bit series of computers.
You are in command of a fighter-ship and your role is to sweep 50 sectors clear of enemy fighters.
Initially, and between waves, you are presented with a 10x5 grid of sectors. The sectors give an indication of enemy strength by means of differing numbers of dots in each sector.
On warping into a sector, you control a set of crosshairs which indicates the fall of shot of your two laser cannons. Your aim is to destroy all the enemy targets in the sector. This is aided through the use of a radar which allows you to locate off-screen targets.
Gorganitor squadrons detected in all sectors of you Star Cluster. Unable to send additional cruisers but have warped four base stations to your Defense Grid. Good Luck...