K4

K4 or K-4 may refer to:

Military

 * Daewoo K4, a South Korean automatic grenade launcher
 * HMS K4, a 1915 British K class submarine
 * K 4 or Norrland Dragoon Regiment, a Swedish Army cavalry regiment
 * K-4 (SLBM), an Indian submarine-launched ballistic missile
 * USS K-4 (SS-35), a 1914 United States Navy K-class submarine

Transport

 * China Railway K3/4
 * K-4 (Kansas highway), a highway in Kansas
 * Kalitta Air, IATA code K4, an American cargo airline
 * LNER Class K4, a British class of 2-6-0 steam locomotives
 * London Buses route K4, a Transport for London contracted bus route
 * PRR K4s or Pennsylvania Railroad Type K4, a class of American 4-6-2 steam locomotives

Other uses

 * K4, a Security company
 * K4, a four-man sprint kayak
 * K4, a model of the British red telephone box
 * K4, a normal modal logic
 * K$4$, in graph theory, the complete graph of four vertices
 * K$4$, in abstract algebra, the Klein four-group
 * K4 (mountain) or Gasherbrum II, a mountain between China and Pakistan
 * Kawai K4, a digital synthesizer made by Kawai Musical Instruments
 * Koalisyon ng Katapatan at Karanasan sa Kinabukasan (K4, Coalition of Truth and Experience for Tomorrow), a Philippine political coalition
 * K4 refers to Kryptos part 4, the last section of the cryptographic puzzle sculpture (currently unsolved)