In Army Defender the player must defend his base against hordes of invading enemies. Players control a turret located at the bottom edge screen. Touching the screen makes the turret fire and there are different kinds of weapons to survive as long as possible.
The opposition consists of soldiers, tanks, parachute troopers, combat helicopters, fighter planes, bombers and elite forces. Somewhat similar to the concept of Ikaruga, enemies come in two types of colours. To hit red enemies, the turret has to be red too. The colour of the turret can be changed with a touch of the Stylus. As a last resort there is also an atomic bomb that clears everything on the screen, but it comes in limited quantity.