The Military Carbine, Experimental Models were a series of experimental submachine guns developed at RSAF Enfield during the 1940s. The aim of the project was to create a suitable replacement for the Sten in British Army service. Six MCEM guns were made in total, but none of the designs were successful and the project was abandoned in 1947.
RSAF Enfield began work on the MCEM project around 1942, and aimed to have finished prototypes ready by the end of the war; the British Army had no intention of keeping the Sten gun in service once the war was over and sought an immediate replacement. Enfield divided its design teams up by nationality and had two separate teams working on the MCEM project: one consisting of British engineers and another consisting of Polish engineers. The British team was headed by Harold J. Turpin, co-designer of the Sten. The Polish team was headed by Lt. Jerzey Podsenkowski.
The British team's first prototype was known as the MCEM-1. Internally the design was similar to that of the Sten. The fire rate was moderated by a spring collar that would grip the bolt every time it traveled back. The wooden buttstock of the MCEM-1 could be detached from the grip. It was fed through two 40-round magazines welded together side-by-side.
The Polish team's first prototype was known as the MCEM-2. It was a compact machine pistol-type weapon and was one of the first submachine guns to feed magazines through the pistol grip. The MCEM-2 utilized a "wrap-around" style bolt with a fixed firing pin, which was cocked through a slot above the end of the barrel. A detachable wireframe buttstock with a canvas covering, which also doubled as a holster, could be fitted. The ejection port was placed just in front of the trigger guard and ejected spent casings straight downward.
The MCEM-3 was the improved version of the MCEM-1. It was given bayonet fittings to meet the British Army's specifications and a single 20-round curved magazine replaced the double magazine feature of the MCEM-1. The regulator system present on the MCEM-1 was also removed.
There is little information available about the MCEM-4. Surviving records indicate it was a suppressed version of the MCEM-2, and was designed by Lt. Kulikowski, the designer of the silenced Sten Mk.IIS.
No information has survived regarding the MCEM-5. It may have been designed by a Mr. Sparc.
The MCEM-6 was the improved version of the MCEM-2, designed by Lt. Ichnatowicz. It featured a slightly longer barrel and heavier bolt, reducing the fire rate to 600rpm, and bayonet fittings were added.
RSAF Enfield staged mock trials to determine which of the MCEM prototypes was worth funding; the winner of these tests was the MCEM-3. It was therefore decided that the MCEM-3 should be submitted to official military trials and all work on the other MCEM prototypes was cancelled.
The MCEM-3 was accepted into troop trials by the British Army, which began in 1947. However, it proved unreliable and overheated easily during tests. It also would have been very costly to mass-produce. All factors considered, the MCEM-3 was deemed inferior to its competitors, primarily the Patchett and the BSA guns.
Rather than further improve the MCEM-3 and resubmit it for the next stage of the military trials, RSAF Enfield decided to cancel the project and allocate more funding towards the development of the EM-2 rifle, which was showing promise in the British Army's rifle trials.