In 1939 HWaA (Hitler's army Weapons command) issued a contract for the development of a "Maschinen karabiner", or machine carbine (MKb for short), chambered for the new 7.92x33 Kurz cartridge, to the company C.G. Haenel Waffen und Fahrrad fabrik. Initial development took place under the designation of MKb.42 - Maschinen karabiner, 1942. The new weapon was intended as a replacement for submachine guns, bolt action rifles and, partly, light machine guns for front troops and was intended to have an effective range of 600 meters or so.
The famous designer Hugo Schmeisser led the Haenel development team, which produced the first working prototypes of new weapon by 1942. In accordance with the specification, the new weapon inherited several features from MP-40 submachine gun, such as the left-side charging handle with slot safety and magazine housing with button release. Because the new weapon had to be made with the maximum usage of stamping and welding, Haenel was joined by the Merz Werke, a company with no knowledge in firearms but a great deal of experience in steel stamping and forming. The first weapons were issued to front line units on the Eastern front by the mid-1942, and the low-rate mass production began in late 1942. A total of about 10,000 MKb.42(H) were produced for the German Army before its production was ceased in favor of an improved design, the MP-43 / Stg.44.
The MKb.42(H) is a gas operated, selective-fire weapon. It uses a long-stroke gas piston, located above the barrel in a long gas tube. The barrel locking is achieved by tipping the rear part of the bolt down into the locking recess, cut in the machined steel insert in the stamped steel receiver. The gun fires from an open bolt at all times, and the only safety is the MP-40 type slot, cut at the rear of the charging handle slot, in which the charging handle can be hooked when the bolt is open. The cross-bolt type fire mode selector is located above the trigger guard. The MKb.42(H) could be fitted with standard bayonet, and has a wooden butt.