There's actually four.
are probably the ones you're thinking of. There's also a component known as the Army of the United States, which is currently inactive, and reserved for times when the draft is implemented.
United States Army's motto is 'This We'll Defend'.
United States Army Corps of Engineers was created in 1775.
United States Army Institute of Heraldry's motto is 'Latin for'.
Sixth United States Army Group ended in 1945.
They fought for the United States (the Union) as opposed to the Confederate States (Confederacy.)
Regular ArmyArmy ReserveArmy National GuardArmy of the United States
The United States Army
United States Army's motto is 'This We'll Defend'.
United States Army Military District of Washington's motto is 'Haec Protegimus'.
Association of the United States Army was created in 1950.
Second United States Army's motto is 'Second To None'.
United States Army Reserve Command's motto is 'Twice the Citizen'.
Sixth United States Army Group was created in 1944.
United States Army Air Service was created in 1918.
United States Army Medical Unit was created in 1956.
United States Army Medical Unit ended in 1969.
United States Army Ordnance Museum was created in 1967.