Many new ways of killing your opponent became available in World War I. In fact, it was called the first “Modern War” because of its availability of new weapons. Poison gas was used for the first time in World War I. This was also the first time that machine guns were used. Germany introduced submarines, calling them U-Boats. Also, World War I was the first time that air planes were used as weapons. Machine guns were attached to them or they dropped a bomb. Heavy artillery was also used for the first time in World War I.