design by Heinrich Vollmer, about 10,000 were manufactured. It was exported to Spain, Mexico, China and Yugoslavia, but also used domestically by the SS, as well as being produced under license in Francoist Spain. World War II Changes in design accelerated during the war, with one major trend being the abandonment of complex and finely made pre-war designs like the Thompson submachine gun to weapons designed for cheap mass production and easy replacement like the M3 Grease Gun. The Italians were among the first to develop submachine guns during World War I. They were slow to produce them under Mussolini; the 9 mm Parabellum Beretta Model 38 (MAB 38) was not available in large numbers until 1943. The MAB 38 was made in a series of improved and simplified models all sharing the same basic layout. The MAB 38 has two triggers, the front for semi-auto and rear for full-auto. Most models use standard wooden stocks, although some models were fitted with an MP40-style under-folding stock and are commonly mistaken for it. The MAB 38 series was extremely robust and proved very popular with both Axis and Allied troops (who used captured MAB 38s). It is considered the most successful and effective Italian small arm of World War II. During the later years of the war, the TZ-45 submachine gun was manufactured in small numbers in the Italian Social Republic. A cheaper alternative to the MAB 38, it also sported an unusual grip safety. In 1939, the Germans introduced the 9 mm Parabellum MP38 which was first used during the invasion of Poland of September that year. The MP38 production was still just starting and only a few thousand were in service at the time. It proved to be far more practical and effective in close-quarters combat than the standard-issue German Karabiner 98k bolt-action rifle. From this experience, the simplified and modernized MP40 (commonly and erroneously referred to as the Schmeisser) was developed and made in large numbers; about a million were made during World War II. The MP40 was lighter than the MP38. It also used more stamped parts, making it faster and cheaper to produce. The MP38 and MP40 were the first SMGs to use plastic furniture and a practical folding stock, which became standard for all future SMG designs. The Germans used a large number of captured Soviet PPSh-41 submachine guns, some were converted to fire 9