The Johnson Semi Auto rifle and light machine gun were invented by one MELVIN Johnson, and had nothing to do with the Iver Johnson company. The M41 rifle was used to a limited extent by the Marine Raider units, as was the LMG. The Marines' use of the Johnson may have been in part an example of Corps loyalty to one of their own, since Mel Johnson had been a Marine corps officer. As noted above most of the Corps pieces had originally been contracted for by the Dutch Govt. for use by their East Indies troops.
I owned a Johnson rifle for several years back in the 1960's. As I recall, Golden State Arms in Calif. had bought a bunch of them from the Dutch, and assembled them here in the States. The piece was short recoil operated, like the old square back Browning shotguns, and the barrel recoilled about 3/4 of an inch when you fired. It had a ten shot rotary mag, loaded from the side thru a slot under the ejection port, using 1903 Springfield clips, or single rounds. The LMG could also be loaded the same way, but generally was loaded by replacing the 25 shot mag that stuck out the left side of the reciever. That mag was a single stack unit, so it stuck out a LONG way.
In 1944, the LMG was redesigned , and the traditional bipod on the barrel was replaced w/ a funky looking monopod type deal, which when folded up comprised the fore end. Barrels on both the rifle and the LMG could be removed in about 30 seconds, which was an advantage on the LMG, but (I think) a disadvantage on the rifle. Inevietably the wear on the barrel retaining surfaces affected accuracy, and I never could get that Johnson of mine to shoot nearly as well as the garden variety M1 I also owned at the time.
All in all, the Johnsons were interesting pieces, but the Marines did the right thing when they mothballed theirs, and went to the M1 and back to the M1918 BAR.