The machine gun:
This was the weapon that brought mass infantry charges to their knees, often literally. The machine gun, which was invented in 1884 by American Hiram Maxim, was used by both sides of the war, often mounted in concrete pillboxes to defend trenches from being stormed by human waves. It was an advance over previous rapid-fire weapons as it used the energy from the recoil to eject each spent cartridge and insert the next one, producing a firing rate of approximately 600 rounds per minute.
However, further advances were needed as Maxim guns were too heavy to be used by advancing infantry. Lighter machine guns, such as the Lewis gun, were developed for offensive roles, such as by the Australian Corps in the Battle of Hamel, France, in 1918.
Imperial War Museum