399th may refer to:
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399th Bombardment Group, inactive United States Air Force unit
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399th Bombardment Squadron or 99th Air Refueling Squadron, part of the 6th Air Mobility Wing at Birmingham Air National Guard Base, Alabama
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399th Fighter Squadron or 57th Weather Reconnaissance Squadron, inactive United States Air Force Reserve squadron
See also
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399 (number)
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399, the year 399 (CCCXCIX) of the Julian calendar
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399 BC
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