You control a ship that fires at a cannon surrounded by three oppositely rotating energy rings of twelve segments each. When a clear line of fire is open, the cannon fires back at your ship with a big "fuzzball". Three sparks start off on the rings, but eventually fly loose and chase the player's ship. In 1981, Zaccaria licensed a clone of Star Castle and released as Space Fortress. Century Electronics also released an arcade title in 1981 as Space Fortress, but it is unrelated to Zaccaria's Star Castle clone.