Sub Chase! was a simple two player game where you played either as a plane or a submarine shooting missiles at each other. The submarine would enter on the lower half of the screen going left to right allowing the player to either go up and down or slow and accelerate. The plane would do the same except it would be on the upper half and going right to left.
The goal was to hit the other player and score a point. As you played, a timer would count down and when the counter reached zero, the player with most points would win.
As an additional hazard, there where neutral ships moving in the middle. Hitting them with the missile would subtract one point from the score. The neutral ships where persistent, so they never sunk.