The Rainbow-class submarines were designed as improved versions of the Parthian class and were intended for long-range operations in the Far East. The submarines had a length of 287 feet 2 inches (87.5 m) overall, a beam of 29 feet 10 inches (9.1 m) and a mean draft of 13 feet 10 inches (4.2 m). They displaced 1,772 long tons (1,800 t) on the surface and 2,030 long tons (2,060 t) submerged. The Rainbow-class submarines had a crew of 56 officers and ratings. They had a diving depth of 300 feet (91.4 m).[1]
For surface running, the boats were powered by two 2,200-brake-horsepower (1,641 kW) diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 660-horsepower (492 kW) electric motor. They could reach 17.5 knots (32.4 km/h; 20.1 mph) on the surface and 9 knots (17 km/h; 10 mph) underwater. On the surface, the boats had a range of 7,050 nautical miles (13,060 km; 8,110 mi) at 9.2 knots (17.0 km/h; 10.6 mph) and 62 nmi (115 km; 71 mi) at 4 knots (7.4 km/h; 4.6 mph) submerged.[1]
Rainbow served in the Far East until 1940, when she moved to the Mediterranean. She left for a patrol off Calabria on 23 September 1940
[4] and was due to be back in Alexandria on 16 October, she was last heard from on 25 September. She is believed to have been sunk on 4 October in a collision with the Italian merchant shipAntonietta Costa, which reported striking a submerged object at 03:30, followed by a huge underwater explosion while sailing in convoy from Albania on that date.[5]
Until 1988 it was believed that Rainbow had been sunk by the Enrico Toti, but eventually it was determined that HMS Triad (N53) was the submarine that Enrico Toti sank.[4]
Akermann, Paul (2002). Encyclopaedia of British Submarines 1901–1955 (reprint of the 1989 ed.). Penzance, Cornwall: Periscope Publishing. ISBN1-904381-05-7.
Bagnasco, Erminio (1977). Submarines of World War Two. Annapolis, Maryland: Naval Institute Press. ISBN0-87021-962-6.