C11, C.XI, C-11 or C.11 may refer to: Transport C-11 Fleetster, a 1920s American light transport aircraft for use of the United States Assistant Secretary of War Fokker C.XI, a 1935 Dutch reconnaissance seaplane LET C-11, a license-build variant of the Soviet Yakovlev Yak-11 trainer aircraft C-11 Gulfstream II, the military designation of the Gulfstream II business jet Barroso (C11), a light cruiser of the Brazilian Navy HMS C11, a 1907 British Royal Navy C class submarine HMS Liverpool (C11), a 1937 British Royal Navy Town class light cruiser JNR Class C11, a class of Japanese steam locomotives USS Marblehead (C-11), an 1892 light cruiser of the United States Navy BSA C11, a British motorcycle manufactured between 1939 and 1956 Mercedes-Benz C11, a 1990 Group C prototype race car London Buses route C11, a public transportation route in England LNER Class C11, a class of British steam locomotives Science and technology C11 (C standard revision), standardized version of the C programming language Head and neck cancer (ICD-10 code) Eye diseases, (MeSH code); see List of MeSH codes (C11) Carbon-11, an unstable isotope of the chemical element Carbon Caldwell 11, the Bubble Nebula, an emission nebula in the constellation Cassiopeia Other uses C11 (rifle), a competition and training weapon used by members of the Royal Canadian Army Cadets C11 Right of Association (Agriculture) Convention, 1921 Bill C-11, various articles of legislation of the Parliament of Canada French Defence (Encyclopaedia of Chess Openings code) 11th century See also 11C (disambiguation)