Good morning, and thanks for the replies :)
It is interesting to note that an American firm came up with the idea. With a patent date of 1918, I would think that the experiences in WW1 would have been the impetus for coming up with it. The Vickers MK1 was a good example of a medium machine gun used in the European theater of WW1, which used .303 ammunition. Although the Americans were late to the war, they likely saw the effectiveness of the Vickers and how bullet proof" (pardon the pun :) ) it was. The Vickers MK1 was then adopted to all roles in WW2 as in fighters, bombers, infantry, trucks and, I believe, tanks as well.
I know one WW2 veteran that I have done work for in the last few years. I should go pay him a visit with one of these. Maybe he can shed some additional light on it. He was involved in the Itallian campaign.