Schull and Skibbereen Railway 4 Erin was a 4-4-0T locomotive manufactured by Nasmyth, Wilson and Company of Patricroft near Manchester in 1888. It was the Schull and Skibbereen Railway's fourth locomotive. In 1925, the railway was absorbed into the Great Southern Railways and renumbered 4S, and placed in Class 4S or Class DN5 as the sole member. Following the GSR classification by wheel arrangement, "D" meaning a locomotive with a 4-4-0 arrangement, "N" meaning Narrow Gauge. The 4-4-0 wheel arrangement is unusual for tank locomotives but more common on narrow gauge than standard.