This is a new one to me. The Marines had access to Browning AN/M2 (or M2 AN) 1919 machine guns from destroyed aircraft. That version of the 1919 fired at a rate of 1200 to 1500 rounds per minute, as opposed to the standard infantry 1919 which fired at a rate 400 to 600 rounds per minute. Moreover, the AN/M2 aircraft version was about 1/3rd lighter than the infantry version. Some gearhead Marines got together and asked the question; why not adapt these scrap guns for our compnay? I'm pretty sure this idea must have been germinated by what they knew of the German MG42 and its high rate of fire. A company of Marines slated for Iwo Jima got together and built a half dozen of them to use against the Japanese pillboxes and entrenchments they knew they'd face on Iwo. Part of the story is told in this vid. I'd like to hear more from our experts here.