Diesel locomotives of Ireland
Although prototype diesel locomotives ran in Britain before World War II, the railways of both the Republic and Northern Ireland changed over much more rapidly from steam to diesel traction than those in Britain, due to the island's limited coal reserves and (in the Republic) an ageing steam locomotive fleet. Northern Ireland operated several diesel shunters as early as the 1930s.
Source: Wikipedia — Diesel locomotives of Ireland (CC BY-SA 4.0)