'SD' (i) was the designation of Allied convoys (together with a numerical and sometimes a literal suffix) plying the route from Iceland to the Clyde river estuary, and as such reciprocals of the 'DS' series (April 1941/May 1945).

The first of the 70 such convoys was SD.1 of 14/16 April 1941 with the 3,244-ton British infantry landing ships Royal Scotsman and Royal Ulsterman escorted by the elderly ex-US destroyers Lancaster and St Mary’s. The last was SD.65 of 12/15 May 1945 with the 14,182-ton Largs Bay escorted by the destroyer Westcott and frigate Rother.