over the regular infantry rifle in urban, mobile, and guerrilla warfare. The MP 18 served with German police and paramilitary forces after the end of the war. It was widely used in combat by the Freikorps Von Epp against the Spartacus League in Bavaria and by other Freikorps in Berlin, where its efficiency in urban combat was demonstrated. During the failed 1924 coup in Estonia the MP18 was used to defend the Tallin barracks from Communist militants; some of which were armed with Thompson submachineguns. This was possibly the first engagement where submachineguns were used on both sides. All the limited conflicts between 1920 and 1940 saw an increasing use of this new class of weapons, first in South America during the Chaco War, then in Europe during the Spanish Civil War, and in China during the Warlord Era and the Japanese invasion, where its use by well-trained Chinese troops was costly for the invaders as in the Battle of Shanghai. It was also used during World War II by various partisans and resistance forces. Since the treaty allowed the Weimar Republic to keep a small quantity of submachine guns for police use, a few hundred MP 18.1s were modified to accept Schmeisser's original 20-round magazine design. This modification, conducted by Haenel Waffenfabrik, required removal of the existing magazine well collar, and replacement with a different one. These weapons were overstamped with the date "1920" on the receiver and magazine well to show they were legitimate weapons owned by the Weimar Republic and not war bringbacks or clandestine weapons. Bergmann sold the licence of the MP 18. 1 to SIG Switzerland; the Swiss made model was known as the SIG Bergmann 1920. It existed in .30 Luger and 7.63 mm Mauser. The Bergmann MP 18.1 represents a milestone both in terms of armament technology and warfare tactics. It opened the way for a whole new class of weapons and triggered the research for lighter automatic firearms to be used by mobile troops. Its first direct competitors did not see service in World War I, but most of them saw use in all the limited conflicts taking place in the inter-war period. Evolution The French, despite being moderately interested by this class of armament because they had designed and introduced in service many semi-automatic and automatic weapons, immediately launched studies based on captured MP 18s. The design of the STA 1922