The main reason the war was so deadly was the combination of new technology and outdated tactics. While we may think about tanks, airplanes, and poison gas, all of which made their debut in the First World War, the two most devastating technologies were American. Machine guns and barbed wire. Attempting to march in lines toward an enemy's trench, soldiers of both sides were mowed down by machine gun fire. According to one German machine gunner at the Battle of Somme in 1916, the British officers went in front. I noticed one of them walking calmly, carrying a walking stick. When we started firing, we just had to load and reload.