Flamethrowers were introduced in WW1. They were used by the Germans to bring pain to the French and British. The first notable use of them was in the battle of Hoogie in Flanderus. They were used in the war to penetrate the enemie's trench defenses. " fun fact. The US made Flamethrowers later and one model the M2 was called, "The finest Flamethrower in WW2!" In ww1 they were by far the most useful weapon of ww1.After seeing the Germans use them, the British became an experimentor on their own Flamethrowers. During the war the Germans used 650 attack with Flamethrowers on the British and French.
Machine guns were introduced too in WW1. They weighed between 30kg through 60 kg. It usually required four to six operators at a time. It was said that they could shoot 400-600 small calibre bullets per minute. However they overheated after two minutes of use. It would take cold air or water to cool them off. However they still jammed up in hot conditions or when used by unexperienced operators. To fix this they lined up multiple machine guns to hold their defensive positions