Fleet numbers 7600–7619 were built and delivered in 1944 and 7620–7629 in 1945, all by the Baldwin Locomotive Works of Philadelphia, Pennsylvania. They went to work on the Cumberland Division's rugged West End subdivision with its more than 2% grades and tight curves, where with the older 2-8-8-0 EL classes, they hauled West Virginia coal and freights. Since the EM-1s had roller bearings throughout, they also handled mail and express trains, replacing two B&O class T-3 4-8-2 Mountains. That continued until January 21, 1947, when near Oakland, Maryland, train 29 with engine 7625 derailed with the locomotive rolling onto the engineer's side, killing the engineer. The EM-1s were then restricted to coal and freight trains until the late 1950s, when the B&O used EM-1 No. 7600 for railfan trips.