These are not American locomotives being imported but British locomotives being exported towards the end of WW1. These are narrow gauge (600 mm) 4-6-0 T tank locomotives built for the War Department by the Hunslet Engine Company of Leeds, more than 150 were built in several batches ordered between 1916 and 1919. Known as 'War Office Tanks' they were a very successful and, relative to their size, powerful locomotives used for transport behind the lines of battle. The nearest one in the photo appears to be War Department no. 2359, one of a batch ordered in 1918 and supplied in 1919. The location appears to be the low level quay at the south side of No.1 Dock at Barry with a length of temporary narrow gauge track laid for storage of the locomotives prior to export.