This is one of the USA Class 0-6-0T locomotives introduced to the Southern Railway in 1942. There were a total of 14 in 1948, on nationalisation. There is a long and detailed article about these on the Kent Rail website, which begins: "This class formed part of a large production run of American shunting tank engines, designed to operate on the railways of Europe after D-Day. The urgency in which they were required led to the quite astonishing feat of a brand new locomotive design being completed and ordered within a single week." They were all withdrawn about 1962, so this picture would I guess have been taken in the 1950s, most probably at Southampton Docks.
Peter Langsdale 10:00, 27-12-2010
This doesn't really look like Southampton docks. After 1962 they were used at various departmental locations around the Southern Region; at least one lasted 'til the last day of steam on the Southern in 1967 having been the shunter at Guildford.