The mechanism of the Maxim gun employed one of the earliest recoil operated firing systems in history. The idea is the energy from the recoil is used, in lieu of a locked bolt or a lever mechanism, to eject each spent cartridge and insert the next one. This made it vastly more efficient and less labour-intensive than previous rapid-firing guns, such as the Gatling, Gardner, or Nordenfelt guns that relied on actual mechanical cranking, as well as decreasing the gas buildup in the barrel, allowing the gun to fire more bullets over an extended period of time without overheating the barrel. The Maxim gun design still required water cooling, however, which gave it additional points of failure and made it more difficult to operate and heavier per calibre, compared to most later heavy machine guns. Trials demonstrated the Maxim could fire 600 rounds per minute. Compared to modern machine guns, the Maxim was heavy, bulky, and awkward. Although a lone soldier could fire the weapon, it was usually operated by a team of men. Apart from the gunner, other crew were needed to speed reload, spot targets, and carry and ready ammunition and water. Several men were needed to move the heavy weapon and mounting.