The C&O turned to the American Locomotive Company to build it some 2-8-2 Mikado type locomotives

Class K-3, also delivered in 1924, assigned road numbers 1210 through1259 and fifty of the third class, delivered in 1926, designated as Class K-3a and given road numbers 2300 through 2349.

All had 63 diameter drivers, Class K-3 and K-3a had 28 x 32 cylinders, all had a 200 psi boiler pressure and the K-3 and K-3a locomotives exerted 67,698 pounds.
There were some differences between each of these classes including a different specification for tenders in each class. The Class 3 and Class 3a firebox was 338 square feet.

The evaporative heating surface was 4,160 square feet and with the superheater the combined heating surface was 5,663 square feet.