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TDY Temporary Duty Yonder (military slang)
A temporary duty assignment (TDA),
also known as "temporary duty travel" (TDT),
"temporary additional duty" (TAD) in the Navy and Marine Corps (or TDI for "temporary duty under instruction", referring to training assignments),
or "temporary duty" (TDY) in the Army and Air Force.
In the U.S. military, the abbreviation "TDY" stands for temporary duty. Temporary duty refers to the situation when a soldier or other employee is assigned to serve at a location that is not his permanent station.
Generally, TDY assignments are shorter than six months in duration. If an assignment lasts longer than that, most organizations consider the assignment to be a permanent change of station. Soldiers can be assigned anywhere for their TDY assignments.