High Quality Content by WIKIPEDIA articles! The Odin class submarine (or "O class") was a class of nine submarines developed and built for the Royal Navy in the 1920s. The prototype HMS Oberon (P21) was followed by two ships originally ordered for the Royal Australian Navy, but transferred to the RN in 1931 because of the poor economic situation in Australia, and six modified boats ordered for the RN. Three modified ships were built for the Chilean Navy as the Capitan O'Brien class submarines in 1929.