'Touchstone' was a British naval exercise to test the defences of East Africa in the aftermath of the Japanese 'C' (ii) naval raid into the Indian Ocean (29/30 August 1942).

As well as validating the defences of East Africa against the possibility of a Japanese seaborne invasion by the landing of Royal Marine and naval parties from the naval force at Tanga and Dar es Salaam on the coast of Tanganyika and on the island of Zanzibar, 'Touchstone' was also designed to provide cover for the operation and a dress rehearsal for the forthcoming 'Stream', 'Line' and 'Jane' landing operations on Madagascar operations.

Operating from Kilindini on the coast of Kenya, the ships involved were the battleships Warspite, Resolution and Valiant, the light cruisers Enterprise, Gambia and Free Dutch Jacob van Heemskerck, and the destroyers Decoy, Fortune, Foxhound, Griffin, Inconstant, Australian Napier and Nepal, and Free Dutch Tjerk Hiddes and Van Galen.