R21

R21, R-21 or R.21 may refer to:

Military

 * R-21 (missile), a Soviet submarine-launched ballistic missile
 * HMAS Melbourne (R21), an aircraft carrier of the Royal Australian Navy
 * HMS Chivalrous (R21), a destroyer of the Royal Navy
 * USS R-21 (SS-98), a submarine of the United States Navy
 * YUGOSLAV DESTROYER Kotor

Roads

 * R-21 regional road (Montenegro)
 * R21 (South Africa)
 * R21 highway (Russia)

Science and medicine

 * Dichlorofluoromethane, a refrigerant
 * R21: Harmful in contact with skin, a risk phrase
 * R21/Matrix-M a Malaria vaccine
 * Small nucleolar RNA R21

Other uses

 * R21 (New York City Subway car)
 * Kwanyama dialect
 * Renault 21, a French family car
 * Tumansky R-21, a Soviet turbojet engine