Keys Z and C move the ship left or right, it says, but hey! Where's the ship?

We have to imagine it, against the background of muted noise as the shots zap home and the invaders evaporate like beeping bats.

Your score is kept and previous highs recorded till stir-passed by the summated efforts of your three lives.

This is really quite a good implementation of the old favourite, but I would be more enthusiastic if I had not seen it so often done rather better by machines with colour and using machine code.

The third expert level would really have to be written in assembler if it is to achieve a noticeable advance on the "fast" level where the Forth is practically flat out.