Many armies use different regimental systems. The United States, among others, uses the parent regiment system.

In this system, regiments are simply there to preserve units' lineage, and few regiments actually are combat bodies (in the United States Army, there are very few remaining infantry, cavalry, or artillery regimental bodies). The exceptions remain the "special" units, such as engineer regiments and armored cavalry regiments. Rather, the regiments are split into battalions (infantry, usually three) or squadrons (cavalry, usually three or more). Artillery can be split into battalions, batteries , or other units, depending on the type. These battalions are the actual combat units. For example, West Point is garrisoned by the 1st Battalion, 1st Infantry . However, the actual unit, the "1st Infantry", technically does not exist in military unit terms.

This system has been adopted only recently (about 1953) by the U.S. Army. Before then, it used the traditional regimental system, where regiments were actual combat units. This change can be viewed in the following examples:

Order of Battle: 1862 US Army

(This is just a fictional example)

1st Cavalry Brigade/1st Cav. Division/ Cav.Corps/ Army of the Potomac

1st United States Cavalry Regiment

3rd United States Cavalry Regiment

24th New York Volunteer Cavalry Regiment

25th New York Volunteer Cavalry Regiment

Battery B, 1st New York Light Artillery Regiment

Order of Battle: 2000 US Army

(This is just a fictional example)

1st Brigade

1st Battalion, 34th Infantry Regiment (Mechanized)

2nd Squadron, 10th Cavalry Regiment

5th Battalion, 6th Air Defense Artillery Regiment

1st Engineer Regiment

24th Logistic Battalion