The GSWR built 90 engines of the 101 Class(J15) and with an additional 20 engines built by Beyer Peacock and Sharp Stewart, the total amount was 110 engines, the largest class in Ireland. They were built for goods services but later used for both goods and passenger services. They were very flexible and were able to travel to most parts of the GSWR and later GSR/CIE network. Two 101 Classes have been preserved by the RPSI, No.184 and 186. Engines rebuilt with a Z type Boiler: 101, 102, 104-108, 110, 114, 118, 120, 122-130, 132, 136-141, 143, 144, 146-149, 151, 153, 154, 156, 158-160, 163, 164, 166, 168, 170-172, 174, 175, 179, 181-183, 185, 186, 188, 192-194, 196-200, 254-256.