A Model 1921 Thompson submachine gun, with a C type drum magazine containing one hundred .45 calibre rounds. This weapon was used by the Irish Republican Army (IRA) during the War of Independence and the Irish Civil War.

The Thompson submachine gun or Tommy gun was invented in America for use in the trenches in WWI. Released after World War I had ended, its high quality construction made it an expensive firearm in a market saturated with surplus low-cost weapons. Tested by Tom Barry in front of Michael Collins at IRA headquarters, the Thompson submachine’s rapid accurate fire and easily concealed removable cartridge made it ideal for guerrilla-style warfare. The IRA was one of the Thompson company’s first customers, however many of the guns in the initial shipment were seized. Eventually 150 Thompson submachine guns were smuggled into Ireland via Liverpool and used during the final stages of the War of independence and throughout the Irish Civil War.

The patina of rust on the gun indicates that this weapon was wrapped in oilcloths and concealed in a hide. Between campaigns, the IRA stored their guns in arms caches in the countryside. This weapon may have been reused during operations in the 1930s, 1940s and 1950s. The Thompson submachine gun continued to be used by the IRA until the early 1970s when it was replaced by the Armalite.