H4, H04, or H-4 may refer to: Science and mathematics ATC code H04 Pancreatic hormones, a subgroup of the Anatomical Therapeutic Chemical Classification System Histamine H4 receptor, a human gene Histone H4, a protein involved in the structure of chromatin in eukaryotic cells Hydrogen-4 (H-4), an isotope of hydrogen H4, a symmetry group in the fifth dimension. Technology H-4 SOW, a precision-guided glide bomb used by the Pakistan Air Force Halo 4, a video game created by 343 Industries for the Xbox 360 Harrison Number Four, an 18th-century marine chronometer designed by John Harrison Zoom H4 Handy Recorder, a handheld digital audio recorder , level 4 heading markup for HTML Web pages, see HTML element#heading Transport Automobiles and roads H4, a halogen headlamp bulb H4, development name of the Hummer HX concept car H-4, shorthand for a 4-cylinder horizontally-opposed or "flat four" engine (not to be confused with an actual H engine) H4 Dansteed Way, a road in Milton Keynes, England Aviation GEN H-4, a Japanese helicopter design Hughes H-4 Hercules (Spruce Goose), the largest flying boat ever built H4, IATA code for Héli Sécurité Helicopter Airlines, based in France H4, IATA code for Inter Islands Airlines, based in Cape Verde Ships and submarines HMS H4, a 1915 British Royal Navy H-class submarine HMS Tenedos (H04), a 1918 British Royal Navy Admiralty S-class destroyer USS H-4 (SS-147), a 1918 United States Navy submarine Rail GNR Class H4, a class of British steam locomotives Other uses H4 (film), a 2013 film H-4 visa, issued by the U.S. Citizenship and Immigration Services British NVC community H4, a heath community in the British National Vegetation Classification system H4 (classification), a cycling classification used in para-cycling H-4, a huge eruption of the Hekla volcano around 2310 BC H4, Houston Hash House Harriers, a social running club based in Houston, Texas See also 4H (disambiguation) HHHH