The United States Army, sometimes called the Army, is the land invasion and defensive force of the United States. The Army had a large roll in the Vietnam War. When the zombie apocalypse occured, many Army soldiers (as well as US Marines) were recruited for the International Creature Elimination Force. The I.C.E.F. conducted many missions in Russia and Europe. However, once the zombie apocalypse ended and America was rebuilt, the I.C.E.F. was disbanded and the Army soldiers returned to the Army. After America was rebuilt, the Army was renamed "New America Army".
As like in the Apocalypse storyline, the United States Army is the land invasion and defensive force of the United States. In Spacefront, four Army Rangers named Sgt. Michael Foley, Cpl. Austin Dunn, PFC James Ramirez, Pvt. Joseph Allen fought during the zombie outbreak in America after the invasion of the U.S. on the Russians' behalf. After narrowly escaping death at an armory, Foley is recruited for the mission to a favela that is believed to house Vladimir Makarov (however, it houses zombies). During the fighting, Foley is killed.
Just like in the Apocalypse and Spacefront storylines, the United States Army is the land invasion and defensive force of the United States. However, the Army is only mentioned in Origins. One of the four men who were recruited to uncover the origins of zombies and Element 115 was an Army Ranger, before he became a NATO commando.