|Play begins after choosing a mission and a stage. Players can choose games or missions in any order. Two players can play at one time.|
Each player begins with a set number of lives. The object of each game is to eliminate aliens or equipment before losing all of one's lives. To successfully complete each mission, players must eliminate a quota of aliens or equipment. At the end of a mission, a player who has lives remaining can select another mission and continue playing.
When either player has no lives remaining, a continue message appears on screen allowing that player to get back into the game by inserting currency. The game is suspended for the remaining player until more currency is inserted or continue time expires, then proceeds for the remaining player from the point
it lett off.
Play may pause from time to time during a particular mission to inform the players of their score and accuracy ratings. A second player can join the game at these times while the game displays a JOIN IN on-screen message.
During the game, players gain points not only by shooting aliens, but also by targeting certain objects. Players should shoot objects as instructed on screen to gain extra points or weaponry.
At various intervals throughout the game, players can acquire extra ammunition or weaponry. Players shoot floating power-up symbols to obtain a more powerful weapon. Shooting certain other targets gains players specific weaponry for the player's arsenal.
Aliens shoot back at players. Each time an alien shoots back successfully, the player loses one life. The player also loses any power-up weaponry. Play continues until all lives are exhausted for both players.
The game has secret rooms, where players can gain more points by shooting targets without being fired upon in return. ln some cases, targets must be shot in a particular order to enter a secret room. When either player opens the door to the secret room, both can gain points by shooting targets.
Players should avoid shooting certain characters wearing blue military uniforms or jumpsuits labeled S.T.A.A.R., an abbreviation of Strategic Tactical Advanced Alien Response. Shooting any of these characters loses a player one life, and eliminates any power-up weaponry acquired.
When play is over, players can enter their initials if they have a high score. If players do not purchase any more credits, the game automatically returns to the attract mode.
Game description from www.arcade-history.com