P31

P31 may refer to:

Aircraft

 * Boulton Paul P.31 Bittern, a British prototype fighter aircraft
 * Curtiss XP-31 Swift, an American experimental fighter aircraft
 * Percival P.31 Proctor, a British radio trainer and communications aircraft

Vessels

 * ARA Drummond, a corvette of the Argentine Navy
 * HMS Uproar (P31), a submarine of the Royal Navy
 * INS Kavaratti (P31), a corvette of the Indian Navy
 * LÉ Eithne (P31), a ship of the Irish Naval Service
 * MALTESE PATROL BOAT P31, of the Armed Forces of Malta

Other uses

 * Makhuwa language
 * Papyrus 31, a biblical manuscript
 * Phosphorus-31 (P-31 or 31P), a stable isotope of phosphorus
 * Pioneer P-31, a failed lunar probe
 * P31, a state regional road in Latvia