S11

S11, S-11, S.XI or S.11 may refer to:

In military 

• Fokker S-11, a two-seat aircraft used primarily as a flight trainer by the air forces of many countries
• HMS Orpheus (S11), a United Kingdom Royal Navy submarine commissioned in 1959
• SPAD S.XI, a French two-seat biplane reconnaissance aircraft of the First World War
• USS S-11 (SS-116), a 1921 S-class submarine of the United States Navy

In transportation 

• S11 (Nissan Silvia), a car
• S11 (Rhine-Ruhr S-Bahn), a public transportation route in Germany
• Expressway S11 (Poland), a partially completed public express route in Poland
• County Route S11 (California), a road in the United States
• LSWR S11 class, a model of steam locomotive
• SABCA S-11, a 1931 Belgian aircraft, one prototype built
• a Hamburg S-Bahn line
• a Stadtbahn Karlsruhe line
• Rans S-11 Pursuit light aircraft

Other 

• S11 (protest), the protests at the meeting of the World Economic Forum in Melbourne, Australia on September 11, 2000.
• September 11, 2001 attacks
• S11 = $ used as a term to describe the US Dollar, the letter S with two lines through it
• S11 postcode, covering areas of south western Sheffield
• British NVC community S11, a swamps and tall-herb fens community in the British National Vegetation Classification system
• an S-Parameter in a 2-port Radio Frequency network
• the name given to the titular Sharktopus in the 2010 Sci Fi Pictures original film.

S₁₁ may refer to :

• a cyclic allotrope of sulfur