Invader Force is a Space Invaders clone. The player moves a laser cannon left and right and has to shoot down all aliens that move back and forth above him while at the same time avoid getting hit by their fire. This variant has the same features as the Taito original including a mother ship that occasionally moves across the top of the screen and shields to hide behind. The game is endless and when all aliens have been killed another (more lethal) wave will take their place. The aim is simply to get as high score as possible. The score per kill depends on the position of the alien. Aliens on the bottom two rows are worth only ten points while those on the top row are worth four times as much. The player has three lives when starting out but an extra life is earned when a full wave has been destroyed. There are six difficulty levels that determine the starting position of the aliens, their descent rate and their firing rate.