United States Army

The United States Army is a playable Faction in Call of Duty, Call of Duty 2, and Call of Duty 3.

Call of Duty
The US Army appeares in Call of Duty in the first campaign. The player controls Pvt. Martin from the 506th Parachute Infantry Regiment. The US Army also appears in the Multiplayer mode of this game.

Call of Duty 2
The US Army appeared once again in Call of Duty 2 in the Battle of Normandry. The player controls Cpl. Bill Taylor from Dog Company and once again, this faction appears in the Multiplayer mode of this game.

Call of Duty 3
The US Army appears again in Call of Duty 3 as the first campaign once again. The player takes control of Pvt. Nichols from the 29th Infantry Division. The US Army appears in the Multiplayer Mode of this game like the previous installments

Call Of Duty:Black Ops
The Army goes on with the 1st Calvary Division.

You didn't look them up on the internet did ya' ;)