This is Gorf by Kevin Gallagher from 1993

Earth is being attacked by the evil Gorfian Robot, your job as a trainee Space Cadet is to stop the Gorfian Empire in its tracks by blasting them to bits with your Space Ship

There are 5 WAVES to overcome, and each time you destroy the flagship, You will level up through Cadet, Captain, Colonel, General, Warrior and finally to Avenger

You have 3 ships to complete this mission, Can you do it, or will you fail? – There is only one way to find out ..

The Game is very similar in gameplay to Space Invaders

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Publisher: Towerbyte Software
Code: Kevin Gallagher