The heaviest Shays belonged to class C and had three two-axle bogies with a service weight of 160 short tons. Likewise, the class D with four bogies up to 150 short tons was offered, which could score with slightly lower power figures with larger reserves and a higher adhesive weight. A common model with three bogies in the 150 ton weight class is presented here. In terms of the number of cylinders, it did not differ from the smallest B-class models, but the cylinders were significantly larger with a diameter of 17 inches and a piston stroke of 18 inches.

The Western Maryland Railway already had one C-70-3 and one D-150-4 type and procured another C-150-3 in 1945. The special thing about this locomotive is that it was the last of about 2,770 Shays built. After the Western Maryland introduced diesel locomotives on main lines beginning in 1949, number 6 was retired in September 1950 after only five years of service. In 1953 it came to the Baltimore & Ohio Transportation Museum and from there it has been on loan to the state of West Virginia since 1980 for use on the Cass Scenic Railroad. It is considered the largest operational Shay today.