What does AE or AA mean in military addresses?

APO AA (APO address, Military APO Address and APO Zip Code serving the Americas) provides APO service to Argentina, Aruba, Bahamas, Barbados, Belize, Bolivia, Brazil, Chile, Colombia, Costa Rica, Dominican Republic, Ecuador, El Salvador, Guatemala, Haiti, Honduras, Nicaragua, Panama, Paraguay, Peru, Puerto Rico, Uruguay, and Venezuela.

AA is short for Armed Forces of the Americas - all branches of the military forces of the United States (Army, Air Force, Coast Guard, Marine Corps and Navy).

APO is short for Army Post Office, which is part of the Military Postal System; it serves land-based military personnel (typically Army and Air Force).

FPO is short for Fleet Post Office and serves water-based soldiers (typically the Navy, Marine Corps and Coast Guard).