People continued to invent new weapons. In 1884 the machine gun was invented, which could shoot many bullets very fast. Soldiers began to use land mines, a bomb hidden in the ground, which explodes when someone walks on it. Small submarines were able to use torpedos to attack bigger ships and hide under the ocean. When airplanes were invented, people began to use them to shoot enemies and to drop bombs on them. They built tanks which had big guns and strong armor. Poison gas was used in World War I but was outlawed and rarely used afterwards. 