O-, P-, and R-class boats for distant patrols

Norman Friedman's figures place the Odin, Parthian, and Rainbow families among the Royal Navy's large long-range patrol submarines. HMS Osiris displaced 1,781 tons surfaced and 2,038 tons submerged, close to contemporary destroyer scale, while its treaty standard displacement was only 1,475 tons. The figures demonstrate why surface, submerged, and treaty standard displacement cannot be interchanged. A range of about 10,000 nautical miles and eight torpedo tubes supported ambush operations at Atlantic and Pacific distances, while some O-class variants ranged farther. Reloads mainly helped a boat survive pursuit after its opening attack, since low underwater speed made a second strike on the same fleet unlikely.