The 'Lewis gun' was a refinement by U.S. Army Colonel Isaac N. Lewis, of an existing design by another American, Samuel McClean. The resulting weapon went on to define the light machine gun as a class of firearm. Machine guns like the Maxim family could fire more continuously and with accuracy at long range, but were heavy and had to be served by a crew of men. A 'light' machine gun would allow soldiers to take the fight to the enemy. The Lewis was designed with a rifle-style shoulder stock, pistol grip, and carrying sling. Instead of a water-filled barrel jacket, the Lewis was air-cooled using a finned radiator fitted beneath a steel shroud. When fired, this created a 'venturi' effect, sucking the hot air forwards and drawing colder air in behind it. This effect can be seen in the accompanying high-speed video footage. The belt feed system of the Maxim was replaced by a rotating 'pan' magazine, limiting capacity but keeping the gun light and easy to handle. Importantly, a clamp-on bipod was also designed to allow a stable firing platform, replacing the fixed tripod mount of the heavy machine guns. Though an American design, the United States Army was reluctant to adopt Colonel Lewis's gun. Instead he turned to Europe.
Use and effect
The British army was the first to adopt the Lewis gun, which became part of important reforms to the deployment of machine guns. The heavy Vickers and Maxim guns, and their gun crews, were taken from the infantry to form the new Machine Gun Corps. The MGC would treat the Vickers more like an artillery piece, delivering fire where it was needed to support the infantry. Meanwhile, infantry regiments instead received the Lewis gun. Firing the same cartridge as the Vickers and with a similar rate of fire, it was far easier for soldiers to carry, get set up, and use in the attack. Along with the Vickers gun, it enabled the changes in tactics that led to later British and Allied success.
The Lewis also became the first ever aircraft machine gun, fitted in flexible mounts on two-seat spotter aircraft, but also mounted above the wing even on later fighters like the SE5a. The cooling radiator was often removed, as cold air rushing over the barrel made it unnecessary. A bigger, 97 round magazine was used to limit the need for frequent and fiddly magazine changes in moving aircraft at freezing altitudes.