The most important weapons of World War I was machine gun. Soldiers dug an elaborate system of trenches to protect against the machine gun. The British introduced the tank, which enabled troops to tear through wires and enemy lines. World War I is also the first war to see significant use of airplanes and submarines. Air battles were called dogfights. The Germans introduced U-boats. Chemical weapons such as poison gas were also used in World War I.
Germany wants to march through Belgium and attack France.