Via the collection of The Museum of the Parachute Regiment & Airborne Forces, we have the Vesely V-43 Machine Carbine.
This 9mm weapon– which used a very interesting double-stack 9mm magazine that was wide and used an extended magazine well, but was capable of holding 60-rounds– was proposed to be issued to airborne forces in the Second World War.
Curiously enough, the V-43, which was designed for Para use, was heavier than the V-42, which was intended for regular “leg” infantry, but the former had the ability to break down into three components (besides mags) for easier storage, say, while jumping out of a perfectly good airplane.
Designed by Free Czech firearms designer Josef Vesely while working out of Birmingham Small Arms, it could fire up to a rate of 1000rpm. It also had a short (8-inch) spike-style bayonet stored above the barrel.
As noted by the Para Museum, “However, it offered very little improvement over the Sten which continued to be issued instead.”
For more info on the Vessley, my homie Ian McCollum over at Forgotten Weapons has a section on it that includes the interesting 35-page manual.