'''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 === * {{Ship|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 * {{Ship|Spanish destroyer|Lepanto|D21}}, a ''Fletcher''-class destroyer of the Spanish Navy
=== Surface vehicles === * Allis-Chalmers D21, an American tractor * Nissan D21, 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
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