From: http://world.guns.ru/smg/smg29-e.htm Thompson Model 1928A1 submachine gun, wartime production (simple, non-adjustable and non-protected rear sight and plain barrel) View attachment 593 The first Thompson gun to see some military use was Model 1928, used by US navy during its expedition in Nicaragua. The so-called "Navy" model 1928 was distinguished by a horizontal forearm that replaced the front grip, and by added sling swivels. With the start of World war 2, US Army procured a large number of Model 1928 submachine guns in "Navy" configuration, marked as US Model 1928A1. These weapons were rather expensive to make, and in 1942 Army adopted a simplified version of M1928A1, known as M1. A little later, an M1A1 version was adopted, which further simplified the design by adoption of a fixed firing pi; otherwise M1A1 were similar to M1 submachine guns. Thomson submachine guns served in US Army well into the Vietnam era, although in limited numbers. American police used Thompson guns until 1970s or 1980s, and few still could be found in some police armories in USA and several other countries of the world. Thompson submachine guns were widely exported commercially prior to and after WW2; Many guns were supplied to Britain and USSR through Lend-lease program during WW2. It must be noted that Soviet troops generally not liked Tommy guns, because of excessive weight and lack of bullet penetration, compared to 7,62mm submachine guns such as PPSh-41 or PPS-43.