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A 'troop' is a military unit, originally a small force of cavalry, subordinate to a squadron and headed by the troop leader. Cavalry soldiers of private rank are called troopers (abbreviated ''Tpr.'', not ''troupers''). Today, ''troop'' has different specific meanings in different armed forces.
Generally, soldiers may be referred to as 'troops'.

Contents

British Army and Royal Marines

Canadian Army

U.S. Cavalry

General military usage

State Police

Collective Noun

British Army and Royal Marines

In the British Army the definition of a 'troop' varies by corps.

★ Household Cavalry and Royal Armoured Corps: Three or four armoured fighting vehicles commanded by a subaltern, oy]]: A unit of two to four guns or launchers, or an equivalent headquarters unit. In the Royal Horse Artillery, a troop used to be the equivalent to a battery in other artillery units.

★ Royal Engineers, Royal Corps of Signals and Royal Logistic Corps: A unit equivalent in size to a platoon in other corps, divided into sections.
Other corps do not use the term.
In the Royal Marines, a troop is the equivalent to an army platoon.

Canadian Army

In the Canadian Army, a Troop is the equivalent of a platoon within the Armoured, Engineer, and Signals branches. Two to four Troops are grouped under a squadron.

U.S. Cavalry

In the United States Army, in the cavalry branch, a troop is the equivalent unit to the infantry company, commanded by a captain and consisting of 3 or 4 platoons, and subordinate to a squadron (battalion).

General military usage

The mass nouns 'troop' or 'troops' can also be used more generally:

★ To refer to all active duty military (e.g. ''Support our troops'', ''Bring the troops home'').

★ To refer to ground forces generally (e.g. ''combat troops'').
Though "troops" is used as a plural noun, "troop" is an incorrect usage for individual soldiers.
When referring to a specific service different words are used (singular or plural):

★ Royal Navy/United States Navy - Sailor

★ Royal Air Force/United States Air Force - Airman

★ British Army/United States Army - Soldier

★ Royal Marines/United States Marine Corps - Marine

★ United States Coast Guard - Coast Guardsman

★ United States National Guard - National Guardsman
Note that within the British Armed Forces, these specific terms are often used only to refer to non-commissioned personnel (an army officer may speak of "my soldiers", for instance).

State Police

Within the United States, State Police forces are often regionally divided into Troops. This usage came about from these organizations modeling themselves off the US Army, and especially the older cavalry units. For this same reason the State Police and Highway Patrol personnel of most states are known as "Trooper" rather than "Officer". California, all US territorial police forces (Guam, US Virgin Islands, Puerto Rico, and the Northern Mariana Islands) and several other states use the "Officer" instead of "Trooper". Most state police and highway patrol forces make much more extensive use of an Army-style rank structure than do local law enforcement agencies.

Collective Noun

The word ''troop'' is also used as a collective noun for any group of primates (including humans).