S31

S31 may refer to:

Aviation

• Blériot-SPAD S.31, a French racing aircraft
• Letov Š-31, a Czechoslovakian fighter aircraft
• Lopez Island Airport, in San Juan County, Washington, United States
• Short S.31, a British bomber prototype
• Sikorsky S-31, an American sesquiplane

Naval vessels

• ARA Salta (S-31), a submarine of the Argentine Navy
• Brazilian submarine Tamoio (S-31)
• HMS Vengeance (S31), a submarine of the Royal Navy
• SMS S31 (1913), a torpedo boat of the Imperial German Navy
• Spanish submarine Almirante García de los Reyes (S31)
• USS S-31 (SS-136), a submarine of the United States Navy

Rail and transit

• S31 (Long Island bus)
• Warabitai Station, a closed station in Oshamambe, Hokkaido, Japan
• S31, a line of the Bern S-Bahn, in Switzerland
• S31, a line of the Hamburg S-Bahn, in Germany

Roads

• Mehran Highway, in Sindh, Pakistan
• County Route S31 (California), United States
• County Route S31 (Bergen County, New Jersey), United States
• U.S. Route 206, partially numbered New Jersey Route S31 until 1953

Other uses

• Sulfur-31, an isotope of sulfur