Built by the GSWR at their works at Inchicore, Dublin, 1913-1914. They were a development from the 249/351 Class(J9) so they were more modern and were even the first class to have superheaters on the GSWR. The class was highly regarded and performed great as a goods engine as well as secondary passenger services. Being used as goods trains over difficult lines including heavy beet trains on the Rosslare-Waterford Line. All engines were high performing except for one, 263, which was a bad steamer. The engine was based in Waterford and a perculiar whistle tone on the 4th beat gave it the nickname, The Whistling Gypsie. The 257 Class' high performance made them the last GSWR engines and the last Irish steam still in working service, until their withdrawal in the 1965.