I don't know. A troop went out with the horse soldier I thought!
I guess the military uses it formally for this From Department of Defense
Definition: (DOD) An approved list of those military units and individuals (including civilians) required for the performance of a particular mission by numbers, organization and equipment, and, in the case of larger commands, by deployment.
Troops is also a slang used to refer to a number of military, like a troop ship!
Troop E, 31st Cavalry
The Cavalry Scouts are equiped with the M-3 Bradley Fighting Vehicle. It is armed with a 25mm main gun, and a 7.62 coaxale machine gun. The Bradley also carries two TOW missiles. The dismounted scouts carry M-16 Rifles, M-203 Grenade launchers, and M-60 machine guns. Scouts employ the use of various types of grenades and mines in the course of a mission. The dismount squad operates mounted with the vehicles as an extention of the platoon leader's eyes and ears. The squad can also operate as an independent reconnaissance squad.
The unit was first organized as Battery A, 464th AAA Battalion. The first commanding officer was Captain Joan Philip Roberts. The first First Sergeant was 1st SGT Andy Anderson and the first AST was Charlie Davenport. The unit was equipped with the 40 mm towed anti-aircraft gun. The unit first met at BB Comer High School until a building was built on Fort Williams Street, the site of the unit's present location. The first permanent armory that was built now servers as the maintenance section area and the motor pool.
The first camp or annual training was in 1948 at Fort Benning, Georgia with 40 men present. The unit received a Certificate of Merit from the D-Day Readiness Force for outstanding achievements in rapidly organizing, recruiting and training. In 1949 Camp was held at Ft. Stewart, Georgia with 80 men present.
On 23 Jan 1951 the unit was called to active duty for the Korean War. On 31 Jan 1951 The unit departed home station with 7 officers and 165 enlisted men for Camp Edwards, Mass. for training. The unit set a record of having the most people ever to be in Sylacuaga was set on that day. On 28 Nov 1951 The unit left Camp Edwards for Camp Roberts, California. On 2 Dec 1951 Attached to Castle AFB, California where the unit was set up around the base for Air Defense. From 6 Dec 1952 - 20 Dec 1952 the unit was transported by military troop train to Ft. McClellan, AL to be outprocessed. After serving on Active Duty for almost two years the unit was released from Active Duty.
Because of a mix-up the 4th Cavalry's horses had been unloaded in Hawaii. Troops E, I and K were mounted on Filipino ponies and participated in the Malolos campaign. The dismounted squadron consisting of Troops C and L participated in the capture of Santa Cruz led by Major General Lawton. (He had served in the 4th Cavalry as a 1st Lieutenant and Captain from 1871 to 1888 and had commanded Troop B during the capture of Geronimo.)