Galaxy Invasion was the second game released by Big Five Software. It was directly inspired by arcade hit Galaxian released one year earlier.

This version includes a special feature not found in the original game: the flagship attack! Sometimes, there is a flagship attack alert. You then have a few seconds to destroy the flagships or they will strike you with their powerful beam (no escape possible)!

Bill Hogue, the programmer, said about Galaxy Invasion:

I'm still really proud of the game play on Galaxy. I was living at my parent's house when I wrote this one and I remember lying in my bed in the darkened room at night watching the glow of the little aliens flying around the screen. Galaxy didn't originally have sound effects but they were added later in a special edition that featured some additional graphic tricks as well. To get sound on a TRS-80 you used a small amplified speaker plugged into the cassette output port. All of the later games I wrote had sound built-in. Super Nova was the only game that never had sound.