MKb 42 Contracts for rifles firing the 7.92x33mm round were sent to both Walther and Haenel (whose design group was headed by Hugo Schmeisser), who were asked to submit prototype weapons under the name Maschinenkarabiner 1942 (MKb 42, literally "machine (ie. fully automatic) carbine"). Both designs were similar, using a gas-operated action, with both semi-automatic and fully automatic firing modes.
The original prototype of Haenel's design, the MKb 42(H), fired from an open bolt and used a striker for firing. The receiver and trigger housing with pistol grip were made from steel stampings, which were attached to the barrel assembly on a hinge, allowing the weapon to be folded open for quick disassembly and cleaning. The Haenel design proved superior to Walther's MKb 42(W), and the army then asked Haenel for another version incorporating a list of minor changes designated MKb 42(H). One was to include lugs for mounting a standard bayonet, another to change the pitch of the rifling. A production run of these modified versions was sent to the field in November 1942, and the users appreciated it with a few reservations. Another set of modifications added a hinged cover over the ejection port to keep it clean in combat, and rails to mount a telescopic sight. A run of these modified MKb 42(H)s in late 1942 and early 1943 produced 11,833 guns for field trials.
Ultimately it was recommended that a hammer firing system operating from a closed bolt similar to Walther's design be incorporated. The gas expansion chamber over the barrel was deemed unnecessary, and was removed from successive designs, as was the underbarrel bayonet lug.
As work moved forward to incorporate this new firing system, development temporarily came to halt when Hitler suspended all new rifle programs due to administrative infighting within the Third Reich, ordered that more, newer submachine guns were to be built and strongly disagreed with the use of the new ammunition. To keep the MKb 42(H) alive, the Waffen Amt (Armament Office) re-designated it into the Maschinenpistole 43 (MP 43) and making a few improvements, billed as an upgrade to existing submachine guns.
This deception was eventually discovered by Adolf Hitler who again had the program halted. In March 1943, he permitted it to recommence for evaluation purposes only. Running for six months until September 1943, the evaluation produced positive results and Hitler allowed the MP 43 program to continue and in order to make mass production possible. The first MP 43s were distributed to the Waffen-SS, and then in October 1943, some were especially issued to the 93rd Infantry Division on the Eastern Front when war was raging. Production and distribution continued to different troops until April 1944, where Hitler ordered it re-designated MP 44 with adding minor updates after taking some interest in the weapon tests. In July 1944, at a meeting of the various army heads about the Eastern Front, when Hitler asked what they needed, a general exclaimed, "More of these new rifles!". This caused some confusion (Hitler's response is reputed to have been "What new rifle?"), but once Hitler was given a chance to see and test-fire the MP 44, he was impressed and gave it the title Sturmgewehr. Seeing the possibility of a propaganda gain, the rifle was again renamed as the StG 44, to highlight the new class of weapon it represented, translated "Storm (Assault) rifle, model 1944", thereby introducing the term.