The Auxiliary Units, Home Guard Shock Squads or GHQ Auxiliary Units were specially trained, highly secret quasi military units created by the British government during the Second World War with the aim of using irregular warfare in response to a possible invasion of the United Kingdom by Nazi Germany, "Operation Sea Lion". With the advantage of having witnessed the rapid fall of several Continental European nations, the United Kingdom was the only country during the war that was able to create a multilayered guerrilla force in anticipation of an invasion.

The Home Guard was an armed citizen militia supporting the British Army during the Second World War. Operational from 1940 to 1944, the Home Guard had 1.5 million local volunteers otherwise ineligible for military service, such as those who were too young or too old to join the regular armed services and those in reserved occupations. Excluding those already in the armed services, the civilian police or civil defence, approximately one in five men were volunteers. Their role was to act as a secondary defence force in case of invasion by the forces of Nazi Germany.