Under extreme circumstances, U.S. military force may be turned against American civilians. An unusually explicit 1945 U.S. military field manual (pdf) described tactics for suppressing riots or protests when State and local officials are unable to control the situation.
“Domestic disturbances are manifestations of civil unrest or tension which take the form of demonstrations or rioting. These public demonstrations or riots may reach such proportions that civil authorities cannot maintain law and order by usual methods. Such disturbances may be caused by agitators, racial strife, controversies between employees and employers concerning wages or working conditions, unemployment, lack of housing or food, or other economic or social conditions.”
“A city held by any organized rioters will be attacked generally in the same manner as one held by enemy troops.”
“When small-arms fire is necessary, troops are instructed to aim low to prevent shots going over the heads of the mob and injuring innocent persons not members of the mob,” the manual said.
For definitional purposes, “a crowd is a large number of persons in a close body.” A “mob is… a crowd whose members, under the stimulus of intense excitement, have lost their sense of reason and respect for law.”
“A mob usually is attacked on the flank, opposite the direction in which it is desired to drive it. When it is apparent that those in front cannot retreat because of pressure from the rear, pressure on the front should be eased temporarily while the rest of the mob is attack with chemical grenades,” the manual advised.
“Bayonets are effective when used against rioters who are able to retreat, but they should not be used against men who are prevented by those behind them from retreating even if they wish to do so.”
The manual, which was originally classified “Restricted,” has long been deemed obsolete and has been superseded by other guidance on military support to civil authorities. It was recently digitized by the Combined Arms Research Library at Fort Leavenworth. See “Domestic Disturbances,” Field Manual 19-15, War Department, July 1945.