The Great Southern and Western Railway Class 101, classified as Class 101 or Class J15 by the Great Southern Railways, was a class of 0-6-0 steam locomotives designed for working goods traffic although they did, and were quite capable of, working branch or even main line passenger trains.The 101s were by far the most numerous class of locomotive (diesel or steam) ever to run in Ireland with 111 being built between 1866 and 1903 with only minor modifications between batches.