The type of weapon used in World War I that greatly changed the nature of warfare was the machine gun. This rapid-fire weapon allowed armies to inflict mass casualties, drastically altering traditional battle tactics. The effectiveness of machine guns contributed to the deadly stalemate of trench warfare, leading to grueling conditions and high mortality rates. As a result, military strategies had to adapt, incorporating new forms of combat, including more strategic movements and the use of tanks and aerial support. The machine gun's introduction marked a significant technological advancement in modern warfare.