After getting his Model 1941 machine gun purchased in small numbers by the US military, Melvin Johnson continued to press for more sales and a general adoption. Following testing results and recommendations from soldiers in the field, he made a number of modifications to the gun and developed the M1944, which was quickly tweaked to become the M1944E1, also called the M1945. This new version included several improvements including:

* Replacing the bipod with a monopod less prone to interfering with barrel removal
* Improved stronger bolt anti-bounce latch
* Metal dual-tube buttstock in place of wood
* and most significantly, a gas-boosted hybrid recoil operating system

This new model of the Johnson was in testing at the end of WWII, and weapons development budget cuts at the conclusion of the war prevented it from replacing the BAR as Johnson and many in the Marine Corps had hoped.

This particular M1945 Johnson is fully transferrable, as came out of the Winchester Museum Collection (now the Cody Firearms Museum) back many years ago when curators would occasionally sell items from the collection to raise money.