In WWI Medic the player is a medic with no weapon or any way of attacking. He can walk or crawl, bandage wounded soldiers, and return wounded allies to the trench. The farther away from the trench that a soldier fell, the more points he is worth when returned. The medic also competes against an enemy medic who is bandaging enemy soldiers. At the end of a game the player medic's total is compared to the enemy medic's, and bonus points are awarded if it is higher.
At irregular intervals a bugle will sound, signifying either an allied or enemy charge. During this time every defending soldier and machine gun will fire, making No Man's Land almost certainly lethal. Randomly bombs and gas canisters will fall from the sky, killing indiscriminately. Airplanes will also strafe the trenches, and will rarely line their aim up correctly to kill almost every soldier in a trench. When the medic is killed or wounded by any source the game is over.
Wounded soldiers will eventually die, but a bandaged soldier will survive indefinitely until he is shot or bombed again. Because the soldiers in the trench are only replaced when a wounded soldier dies or is returned to the trench it is in the player's interest to abandon casualties that they do not intend to save, and to bandage enemy soldiers who are too far away form the enemy trench for their medic to save. In this way the medic is instrumental to the war effort.
If the allied soldiers manage to overrun the enemy trench then the screen moves up to a new No Man's Land. The game will only end with the medic's death.