As you can see, there are two different ways for two players to enjoy the game together. The top left option is for simultaneous, free roaming play. In this mode, both the red and green ships are autonomous, and can fly around the screen however they like. So how does friendly fire work? Let's say red accidentally tags green with a shot; green doesn't lose a life, but their ship blinks and reappears somewhere else. Not quite as co-op as disabling friendly fire entirely, but an interesting compromise, nonetheless.
Space Duel also fixes one of the biggest issues with simultaneous multiplayer games in general: what happens when your buddy has plenty of lives left, but you die early? In many games, even those developed far later than 1982, you are simply out of luck and forced to watch. In Space Duel, as long as one player has a life remaining, the other player always respawns. The only drawback is the respawning player has a damaged ship, which is slower to fire, turn, and thrust. It's an elegant solution to a problem, once that many more games should have taken inspiration from.
So what about the other 2 player mode, with the yellow line connecting the ships? The connecting line, known as a fuse, is like a lifeline between the two players. While they can still thrust, fire, and use shields on their own, they are affected by the other player's choices. This makes for some interesting moments, to say the least. So why is the line between the ships called a fuse? When one player dies, the line begins to burn away, like a fuse on dynamite, until the other player explodes too! You might wonder why you'd ever play in fuse mode, as there are many disadvantages. The primary reason is shields. Both players have far more shield energy available when playing in connected mode, which allows them to stay alive longer. Fuse mode is certainly an amusing and unique twist to the genre.
Space Duel is an interesting game from many different perspectives. Color vector graphic games are few in number, to begin with, and the incredible cabinet artwork makes it even more appealing to collectors. It also has a unique place in the history of cooperative games, with not one, but two modes that allow players to work together. While it may not have the name recognition of its predecessors, Space Duel eclipses them both in many ways. It is a great example of a very early Co-Op Classic.