The Auxiliary Units or GHQ Auxiliary Units were specially trained, highly secret units created by the United Kingdom government during the Second World War, with the aim using irregular warfare to help combat any invasion of the United Kingdom by Nazi Germany, which the Germans codenamed Operation Sea Lion. With the advantage of having witnessed the rapid fall of several continental nations, the United Kingdom was the only country during the war that was able to create a multi-layered guerrilla and  resistance movement in anticipation of an invasion. The Auxiliary Units would fight as uniformed guerrillas during the military campaign, but were not themselves a resistance organisation. If defeated, then resistance units organised by SIS (MI6) would continue the struggle. Service in the Auxiliary Units was expected to be highly dangerous, with a projected life expectancy of just 12 days for its members; along with orders to either shoot each other or use explosives to kill themselves if capture by an enemy force seemed likely.