The MKb 42(H) was the prehistorical Stg-44.
In December 1940, a prototype rifle from Haenel and Walther was tested by the HWA at Kummersdorf. It had multiple jams, several barrels got bulged, and one had a catastrophic failure. Testers blamed the results on poor quality ammunition. In February 1942, 10 million 7.92 mm rounds were ordered for field testing. On 9 July 1942, field and comparative tests were conducted with the ammunition and Haenel MKb 42(H) rifle. 3,654 shots were fired; 11 cases were separated, 67 rounds were duds (56 fired on second trial), and many other rounds stovepipe jammed. Failures were blamed on the prototype stage of the weapon's design.
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.
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.
By March 1943, 2734 MKb 42(H) were accepted into service, followed by 2179 in April alone and 3044 in May; these numbers correlate well with the Haenel estimates for these months (2000 and respectively 3000). Additionally, Haenel estimated that 3,000 were made in June and 1,000 in July, resulting in a high estimate of 12,000 units for the MKb 42(H). However, the Haenel production figures from June 1943 onward do not differentiate between the last batches of MKb 42(H) and the first batches of MP 43/1. Other sources seem to accept only the more conservative estimate of 8,000 units. How many Walther MKb 42(W) were produced is even more uncertain. Some sources suggested as many as 8,000, but conservative estimates put the number at about 200, and say that most of these remained in the Walther factory until the end of the war. Production began in November 1942 and was to reach 10,000 per month by March 1943. The total number of MKb42(H)s manufactured between November 1942 and September 1943 was 12,000 rifles, with only about 1,000 produced per month.
The MKb 42(H) was mostly used on the Eastern front. By one account, the gun saw action as early as April 1942 when 35 of the only 50 prototypes then in existence were parachuted into the Kholm Pocket, where it was apparently instrumental in holding the Soviets back.