The United States Army is the Main Ground Force of the United States. They have been in existence since before the Revolutionary War. The US Army has Been in every war that America has Participated in, from the Revolutionary War up to Operation: Iraqi Freedom, or the Iraq War.
The Army Has Both Ground Forces and Air Forces, with more in the former than the latter. The Air Forces primarily consists of hielocopters,with the pilot generally being a Warrant Officer.
The Formations go as follows, from Smallest to biggest: