There were several types of columns used by the military infantry: marching columns for transiting long distances and columns used on the battlefield. They were not intended as assault formations, except under special circumstances. Reference to a ‘Fifth Column’ dates to the Spanish Civil War (1936–39) and refers to a group or faction of subversive agents (or spys.)
The term ‘Fifth Column’ survived that war and has ever since been used to designate secret armies or groups of armed subversives. With Japan’s surprise attack on Pearl Harbor, fear of the ‘Fifth Column” hit home. A report commissioned by Congress contended that the vast majority of Japanese Americans were loyal but it did nothing to stop the mounting public hysteria and government and military reactionism.