RO2

RO2 can stand for one of the following:
 * Red Orchestra 2: Heroes of Stalingrad
 * Ragnarok Online 2: Legend of the Second
 * Ragnarok Online 2: The Gate of the World, the cancelled version of the above game
 * Organic peroxide or other compounds with the peroxide group
 * JAPANESE SUBMARINE Ro-2, an Imperial Japanese Navy submarine commissioned in 1920 and stricken in 1932