combat by Swedish troops as part of the United Nations Operation in the Congo, during the Congo Crisis during the early 1960s. Battlefield reports of the lack of penetrative power of the 9 mm Parabellum during this operation led to Sweden developing a more powerful 9 mm round designated "9 mm m/39B". In 1946, Denmark introduced the Madsen M-46, and in 1950, an improved model the Madsen M-50. These 9 mm Parabellum stamped steel SMGs featured a unique clamshell type design, a side folding stock and a grip-safety on the magazine housing. The Madsen was widely exported and especially popular in Latin America, with variants made by several countries. In 1948, Czechoslovakia introduced the Sa vz. 23 series. This 9 mm Parabellum SMG introduced several innovations: a progressive trigger for selecting between semi-automatic and full auto fire, a telescoping bolt that extends forward wrapping around the barrel and a vertical handgrip housing the magazine and trigger mechanism. The vz. 23 series was widely exported and especially popular in Africa and the Middle East with variants made by several countries. The vz. 23 inspired the development of the Uzi submachine gun. In 1949, France introduced the MAT-49 to replace the hodgepodge of French, American, British, German and Italian SMGs in French service after World War II. The 9 mm Parabellum MAT-49 is an inexpensive stamped steel SMG with a telescoping wire stock, a pronounced folding magazine housing and a grip safety. This "wildebeast like design" proved to be an extremely reliable and effective SMG, and was used by the French well into the 1980s. It was also widely exported to Africa, Asia and the Middle East. 1950s In 1954, Israel introduced a 9 mm Parabellum open-bolt, blowback-operated submachine gun called the Uzi (after its designer Uziel Gal). The Uzi was one of the first weapons to use a telescoping bolt design with the magazine housed in the pistol grip for a shorter weapon. The Uzi has become the most popular submachine gun in the world, with over 10 million units sold, more than any other submachine gun. In 1959, Beretta introduced the Model 12. This 9 mm Parabellum submachine gun was a complete break with previous Beretta designs. It is a small, compact, very well made SMG and among the first to use a telescoping bolt design. The M12 was designed for mass production and was made largely of stamped steel