Still, there are some features in Space Invaders II that encourage cooperation. Being able to shoot on friend's invaders is one. A good strategy would be to clear all but a few invaders on your own side, then concentrate on helping the other player. The ol' "you take this half" routine that works so well in many other classic co-op titles is a good technique here, too, since you don't want to take out your friend on accident. (Unless you need another life, that is!) Don't take too long, or up to two UFOs will fly through the center of the screen, and drop off another line full of invaders!
The most compelling argument for considering Space Invaders II as a co-op game is an inclusion that was far, far ahead of it's time. If player two lost all lives, the invaders on that side of the screen would move back and forth, endlessly. Player one could take down all of those leftover aliens, and if he had enough lives in reserve, player two would respawn! Just like Contra, but half a decade earlier! This same concept of reviving a fallen partner is an important part of even the latest games, such as Left 4 Dead and Gears of War 2.
Space Invaders II is a truly interesting game, and very unusual in many ways. It took what was fun and exciting about the original, changed things around, and added in some features that were unmatched for many years in the genre. Simultaneous play, the mirrored field, and the possibility of sharing lives with a friend were cutting edge. Space Invaders II is the earliest co-op game we've uncovered to date, and is quite deserving of a bit of love from fans of classic co-op games.