John Browning’s original Model 1895 gas-lever machine gun was still in production by Colt when World War One broke out. It was not the most modern gun around by then, but it was available – and that was the most important feature for many potential buyers. Colt, however, had a lot of other larger orders to fill, and so in 1914 it arranged to subcontract the 1895 pattern gun to Marlin. Marlin (which reorganized to become Marlin-Rockwell in 1916) had a talented Swedish designer named Carl Gustav Swebelius who substantially modernized the design by redesigning it to use a straight gas piston instead of the original swinging lever. This, and its closed-bolt firing, made it a candidate for synchronized aircraft use.
After some further revisions to improve extraction, the gun was designated the 7 MG (model 1917) by the US, and some 38,000 were ordered. At some point the heavy barrel was replaced with a thinner, smooth profile barrel and the cocking handle changed from a loop to a simple “L” handle. In 1918, a new design of hydraulic synchronizer was adopted, resulting in a new designation of 8 MG. At the very end of the war, the Marlin was chosen for use in American light tanks, and 2,646 were converted for that purpose by installing Lewis-type barrel cooling shrouds and flash hiders. None of these reached Europe in time to see service during the war, though.
The Marlin 1917 machine gun is one of the least appreciated and understood of American military machine guns, and detailed information on them is quite sparse. This video was done with he best set of facts I was able to find, and I hope it is not wrong in any substantial area!