ARMY

Capitalize when preceded by the name of a country (as long as army is part of the official name) or when the name is well established:

United States Army British Eighth Army

Russian Army Red Army

People's Liberation Army

Iraqi Army

but Israeli army, Japanese army (army is descriptive in these instances, not the official name)

When army is used by itself, capitalize in references to the U.S. Army, but lowercase such references to any foreign army.

Spell out units through Ninth.

United States Army, the Army, Army officer

the 19th Army, the army

the Indian Army, the army, army officer

Red Army, the army

Union Army, Grant's army, Confederate Army

Army of the Potomac, the army

For Army ranks and abbreviations see MILITARY RANKS.