The Turpin Military Carbine Experimental Model was a British submachine gun designed by Harold J. Turpin, one of the designers behind the STEN gun. Turpin's MCEM was designed in 1945 and was created in an attempt to replace the STEN gun in British service.
The Design Department of Enfield aimed to create a suitable submachine gun to suit the needs of the new General Staff Specifications that had been introduced in April 1945. This required that a submachine gun for the British Army was to fire at no more than 600 rounds per minute, have bayonet fittings for the British No.5 bayonet, have a magazine capacity of 30-60 rounds, and weigh no more than 6lb unloaded. Enfield's Design Department was then split into different sections; there were teams of Polish designers working on rifles and submachine guns, Belgian designers working only on rifles, and British designers who worked on all areas. Turpin headed the British design team, and there was considerable rivalry between the British and Polish teams to produce the best submachine gun. Turpin's team finished theirs first. It was a submachine gun with a machined steel body and a STEN trigger mechanism. It had a right-hand cocking handle which sealed off the cocking slot. It also had a double side-by-side magazine which slid from one end to the other with ease, so the magazine did not even need to be removed in order to reload. Unfortunately it did not have bayonet fittings and thus it did not meet the GS Specifications.
Later, the weapon was improved as the MCEM3. The unique magazine of the MCEM1 was removed in favour of a curved 20-round magazine. The safety catch was moved to the right side of the trigger housing. Bayonet fittings were added for the No.9 bayonet. This model was submitted into trials in September 1946, and was considered to "show considerable promise as being both a efficient and reliable carbine, worthy of more intensive trials". The Polish team's MCEM6 was rejected so that further development could be made on the MCEM3. It was tested in June 1947 against the BSA Machine Carbine, but the MCEM3 was slightly over the weight specifications and fired at 650rpm rather than the recommended 600rpm. The final trials from the 8th - 16th of September resulted in the cancellation of the MCEM3; the handguard got so hot during continuous firing that it could not be gripped without burning the firer.