421st may refer to:

• 421st Air Refueling Squadron, inactive United States Air Force unit
• 421st Assault Aviation Regiment, original name of the Yugoslav 107th Mixed Aviation Regiment
• 421st Bombardment Squadron, inactive United States Air Force unit
• 421st Fighter Squadron (421 FS), part of the 388th Fighter Wing at Hill Air Force Base, Utah

• 421 (number)
• 421, the year 421 (CDXXI) of the Julian calendar
• 421 BC

Topics referred to by the same term

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