Featuring a centrally mounted, vertical boiler, the ‘Y1’ and ‘Y3’ locomotives employed a chain drive system, similar to the arrangement installed on the steam road lorries produced from the early 1900s by Sentinel Ltd
Each of the ‘Big Four’ railway companies experimented with the Sentinel ‘Central Engine’ locomotive, as the chain drive system reduced stress on the rails, lending the locomotives to branch lines, light railways, dockyards and other locations where the track and infrastructure was not of a high standard.