C3, C-3, C.3, C03, C.III or C-III may refer to: Life and biology C3 carbon fixation in plants C3-convertase, an enzyme Complement component 3, a protein of the innate immune system Apolipoprotein C3, a human very low density lipoprotein ATC code C03 Diuretics, a subgroup of the Anatomical Therapeutic Chemical Classification System Castavinol C3, a natural phenolic compound found in red wines Cytochrome-c3 hydrogenase, an enzyme Haplogroup C-M217, called C3 in older publications In human anatomy, C3 may refer to: Cervical vertebra 3, one of the cervical vertebrae of the vertebral column Cervical spinal nerve 3 Clinical Cell Culture, a medical technology company C03, Malignant neoplasm of gum ICD-10 code C3 Collaborating for Health, a health-promotion NGO C3: an EEG electrode site according to the 10-20 system Military C3, Command, control, and communications, a military concept C-3 (plastic explosive), a plastic explosive related to C4 C-3, a United States military designation for the Ford Trimotor the designation for several German World War I and World War II armed reconnaissance aircraft AEG C.III AGO C.III, a reconnaissance biplane of World War I Albatros C.III DFW C.III, a DFW aircraft NAG C.III, an engine powering the Gotha G.IV aircraft C-3, a U.S. military transport version of the Martin 4-0-4 Type C3 submarine (disambiguation), a World War II Imperial Japanese Navy cargo carrier submarine Spanish submarine C-3 HMS C3, a 1906 British C class submarine Type C3-class ship, a type of merchant cargo ships of United States Maritime Commission "C" design USS C-3 (SS-14), a 1909 United States C class submarine USS Baltimore (C-3), an 1888 protected cruiser of the United States Navy Garda Crime and Security Branch (CSB), domestic security agency of Ireland's national police, also known as "C3" C3 Howitzer, a lengthened variant of the M101 used by the Canadian Armed Forces Technology C3, characteristic energy, in astrodynamics, a measure of the rocket energy for an interplanetary mission that requires attaining an orbital velocity above escape velocity C3, the chemical symbol for Tricarbon Cyclopropatriene C3.ai, an AI company founded by Thomas Siebel C3 linearization, a computer science algorithm for resolving the order of method resolution in multiple inheritance conditions Delfi-C3, a Dutch CubeSat satellite Saturn C-3, a 1960 rocket in the Saturn C series Chaos Communication Congress, the biggest annual hacker event in Europe Chrysler Comprehensive Compensation System, important in the development of Extreme Programming VIA C3, a computer processor Creatures