The Plymouth CR-8 was a class of 4-axle B'B' centre cab locomotive, built by Plymouth Locomotive Works in the United States, several of which were used on industrial sites.
Ten units (CR-8b) were briefly operated in Thailand in the mid-1960s. During the Vietnam War they were operated by the US Army in South Vietnam, and afterward became entered Vietnam Railways service as class D10H. A second class of Chinese-built locomotives, classed DFH21, have operated as D10H in Vietnam from around 1980 onwards.
The CR-8 class was available in weights from , with installed power ranging from using hydraulic twin engines via a cardan shaft final drive, in gauges from to .
The gauge American locomotives used in Vietnam used two General Motors 12V71 two stroke V12 engines.
The locomotives were originally thought to have been operated on the Royal State Railways of Siam (RSR) as numbers 2001-2010 beginning in 1963 or 1964. They were transferred to South Vietnam in the late 1960s during the US involvement in the Vietnam War, and operated as numbers 1988 to 1997 by the US Army. After the war's end in 1975 they were reclassified D10H and renumbered 31 to 40 by Vietnam Railways.
Several similar locomotives were used in the US by industrial operators, as well as MBTA and BART. A heavier model, the CR-8XT, was used by companies including Bethlehem Steel and the Jones and Laughlin Steel Company.