The 9x25 mm Danuvia submachine guns (Király géppisztoly) were designed by Hungarian engineer Pál Király in the late 1930s. They were issued to Hungarian army troops in 1939 and remained in service throughout World War II until the early 1950s. A total of roughly 8,000 were made between 1943 and 1945. The Danuvia was a large, sturdy weapon, similar to a carbine. Although inspired by the 9x19mm Parabellum Beretta Model 38/42, the Danuvia used the more powerful 9×25mm Mauser round. Like the Beretta, the Danuvia's magazine can be folded forward into a recess in the stock where a plate then slides over it. The original Danuvia was the 39M, but it was redesigned in 1943 as the 43M. This, the most common version, had a shortened barrel and was provided with a forward-angled magazine. It had a folding metal buttstock and wood forestock fitted with a pistol grip. The Danuvia featured a patented two-part delayed blowback bolt. The fire selector switch is a circular cap on the rear of the receiver and is rotated to one of three settings: E (Egyes)(semiautomatic fire), S(Sorozat) (full automatic), or Z (Zárt)(the safety setting). The ejection port and cocking handle are on the right side of the receiver. It had a ramp-type rear sight above the ejection port and a post foresight at end of the barrel.
Mechanized units found the 39.M too long, so Pál Király and his team, including designers József Kucher and Gyárik, modified it. The design was done in October 1942 and was approved next year as the 43.Minta. The 43.M, is essentially the same as the 39.M, but with a folding metal stock. A pistol grip was added. The ejector was moved from the receiver into the bolt CARRIER. Wooden strips are installed on both sides of the metal frame/receiver. The magazine of the 43.M is canted slightly forward when in the fixed position as opposed to the straight vertical position of the 39.M magazine, and the barrel of the 43.M is approximately 75mm [3"] shorter than that of the 39.M. The magazines of the 39.M and 43.M are not interchangeable. The 43.M was issued with a redesigned sling.
In mid-1944 several internal parts were re-designed to simplify manufacturing. The new gun were called 'Sulyzáras' (Weight-lock) 43.M. Existing guns could be easily UPDATED by replacing their bolt assembly. The gun was well-liked by troops it was issued to; it reportedly functioned well in the sub-zero, muddy conditions on the Eastern Front. The only difficulty was the availability of 9x25mm Mauser ammunition. It was used by the Hungarian army, military police and police forces and stayed in service until the early 1950's when it was gradually replaced by the PPSh-41 and the Kucher K1.