During World War II, after the Royal Navy’s traumatic departure from the Pacific Ocean in early 1942, the 4th Submarine Flotilla and its depot ship, the HMS Adamant, operated with the Eastern Fleet based at Trincomalee––a large, natural harbor located on the coast of Sri Lanka in the heart of the Indian Ocean. Dutch submarines joined them and were placed under British operational control after the fall of the Dutch East Indies to the Japanese.
The number of boats making up British submarine operations in the Pacific remained small, sometimes no more than four at any one time, until after the Italian surrender in September 1943 when reinforcements began to be deployed to the Indian Ocean. By late 1944 a maximum of 40 submarines were active with the Eastern Fleet. However, the length of individual boat deployment was limited by the fact that they could not be refitted in India and had to return to Britain for major repairs.
During all of 1944 through January 1945, three British subs were sunk and one severely damaged by enemy action in the Indian Ocean. In September 1944 British submarines commenced combat patrols in the Pacific under the command of Vice Admiral Thomas. C. Kinkaid, commander of the U.S. Seventh Fleet.
Since British subs were smaller and had less endurance than American boats, they were considered more suitable for inshore operations in the Southwest Pacific. By this stage of the war the force had grown to three flotillas: the 2nd, 4th, and 8th. The last moved to Fremantle, Australia, and comprised six “S” and three “T’ class vessels. The former operated in the Java Sea, the latter in the Sea of China.
The “S “ class had a speed of 10 nautical knots and a range of up to 7,000 miles and carried enough supplies on board to allow it to remain at sea for 30 days. “T” class subs, having roughly the same performance capability as the latest American submarines, could cover 12,000 miles and stay at sea for 50 days.
American subs had been based at Fremantle since 1942, and the 8th Flotilla had to fit in with the established American routines and practices. This was greatly facilitated when the U.S. Navy made available to their British counterparts Fremantle’s repair facilities as well as two U.S. Navy submarine tenders.