D21

D21 may refer to:

Vehicles

Aircraft

• Dewoitine D.21, a French fighter
• Fokker D.XXI, a Dutch fighter
• Lockheed D-21, an American reconnaissance drone
• Salmson D21 Phrygane, a French utility aircraft

Ships

• ARV Zulia (D-21), a Nueva Esparta-class destroyer of the Venezuelan Navy
• HMS Norfolk (D21), a County-class destroyer of the Royal Navy
• HMS Quickmatch (D21), a Q-class destroyer of the Royal Navy
• HMS Shah (D21), a Ruler-class escort aircraft carrier of the Royal Navy
• HMS Wryneck (D21), a W-class destroyer of the Royal Navy
• Spanish destroyer Lepanto (D21), a Fletcher-class destroyer of the Spanish Navy

Surface vehicles

• Allis-Chalmers D21, an American tractor
• D21 Navara, a Nissan Datsun pickup truck
• LNER Class D21, a class of British steam locomotives

Other uses

• Arriflex D-21, a digital motion picture camera
• Chondroma
• D21 road (Croatia)
• D21 – Janeček method, an electoral system
• D21, a computer from Datasaab
• D-21 Special, a guitar made by Martin Guitar