cocking handle to be pushed inwards to lock the closed bolt to the tubular receiver casing. This design change prevented accidental discharges when the bolt was left forward and a loaded magazine was inserted. Operation The MP 18 submachine gun is a simple blowback operated weapon firing from the open bolt. The original MP 18.1 was designed to use the snail drum magazine of the Luger Artillery model pistol. This rotary design type of magazine holds 32 rounds of 9 mm Parabellum, the user having to load the magazine with a proprietary loading tool. A special sleeve was required when the snail drum was used on the MP 18 to stop the snail drum from being inserted too far in the magazine well. After 1920, the MP 18 was modified to use a straight magazine similar to those used in the later developed MP 40 submachine gun. The MP 18 could only fire in the fully automatic mode. Its successor, the MP 28/2, received a modified mechanism with a selector for single shot or fully automatic fire. Users : MP-28 produced under license and adopted as MI-34 (Mitraillette Modèle 1934) :MP18, MP-28, SIG Bergmann 1920 :MP-28 adopted by the São Paulo police in 1934, and still in use in the late 70s The MP18 was used by the Pernambuco police, a MP18 with a 50-round magazine was borrowed by Lieutenant João Bezerra of the Alagoas police and used in the 1938 Angico Raid where Lampião was killed : Some evidence that captured MP 18s in use with Alberta Provincial Police : Used locally made versions of the MP 18, MP 28 and Swiss-made SIG Bergmann 1920 in 7.63×25mm Mauser : MP-28s were likely either purchased as surplus or given as aid by Nazi Germany. Two Ethiopian MP/28s in British possession would inspire the later Lanchester submachine gun. :The MP18 was used to defend the Tallin barracks during the 1924 communist uprising Estonian police purchased an unknown amount of guns from the Finnish Lindelöf factory : 1,523 SIG M/20s in 7.65×21mm Luger were bought between 1922 and 1940 During the Winter War, 171 MP-28s were bought from Belgium; but they did not arrive in time. These guns were later issued in the Continuation War to units in Lapland, home front troops and supply corps. The Leonard Lindelöf company started to manufacture licensed copies of the M/20 in 1922 it is estimated