R4

R4, R04, R.4, R-4, or R/4 may refer to:

Aircraft

 * Caudron R.4, World War I French reconnaissance aircraft, first flown in 1915
 * Curtiss R-4, air ambulance version of the American Curtiss Model R utility aircraft, first flown in 1915
 * Sikorsky R-4, American helicopter, first flown in 1942

Ships

 * HMCS Cayuga (R04), Royal Canadian Navy destroyer
 * USS R-4 (SS-81), U.S. Navy submarine

Weapons

 * R4 assault rifle, produced by South African manufacturer Vektor
 * Remington R4 carbine, assault rifle used by the Philippine Marine Corps
 * Bisnovat R-4, Soviet missile

Other military

 * Plan R 4, the World War II British plan for an invasion of the neutral state of Norway in April 1940

Science

 * R4, designation of risk phrase "Forms very sensitive explosive metallic compounds"
 * R4 nuclear reactor, the fourth nuclear reactor built in Sweden
 * Exotic R4, in mathematics, a differentiable manifold

Cars

 * R4, abbreviation for rear-engine, four-wheel drive layout
 * R4, a sub-class of Group R rally cars
 * Jaguar R4, Jaguar Racing's car for the 2003 Formula One season
 * McRae R4, a rally car designed in part by Colin McRae
 * Renault R4, alternative name for the Renault 4
 * Suzuki GSX-R/4, a concept car made by Suzuki in 2001

Roads

 * R4 ring road in Ghent, Belgium
 * R4 expressway (Czech Republic)
 * R4 expressway (Slovakia)
 * R-4 motorway (Spain)
 * R4 road (Zimbabwe), a road connecting Harare and Nyamapanda
 * Radial Road 4 or R-4, an arterial road of Manila, Philippines

Other transportation

 * R4 (Canberra), a bus route in Canberra, Australia
 * R4 (New York City Subway car)
 * R4 (RER Vaud), an S-Bahn line in the canton of Vaud
 * R4 (Rodalies de Catalunya), a commuter rail line in Barcelona, Catalonia, Spain
 * R4 41st Avenue RapidBus, an express bus service in Vancouver, BC, Canada

Video games

 * R4: Ridge Racer Type 4, a racing game for Sony PlayStation, developed by Namco
 * Rush Rush Rally Racing, a racing game for Sega Dreamcast, developed by Senile Team
 * R4 cartridge, a Nintendo DS flash cartridge

Other uses

 * BBC Radio 4 the premier BBC speech radio station
 * R4, a building in the Norwegian Government quarter (Norw. Regjeringskvartalet)
 * Region 4, the DVD region code for most of Mexico, Central America, South America, Australia, New Zealand, Oceania