steam locomotive dr syn on the romney hythe and dymchurch railway T he Romney, Hythe & Dymchurch Railway's No. 10 Doctor Syn is a distinguished 15-inch gauge steam locomotive with a rich history. Built in 1931 by the Yorkshire Engine Company, it was originally named Black Prince. Post-World War II, the locomotive was renamed Doctor Syn, honoring the fictional smuggling vicar from Russell Thorndike’s novels set in Romney Marsh .