Homestake Mining Company Locomotive Number 9 was purchased in 1907 from the H.K. Porter Company of Pittsburgh, Pennsylvania, as Porter number 3847. Powered by compressed air, it used a large air tank with a capacity of approximately 135 cubic feet of air at 1000 pounds per square inch, filled from a large stationary air compressor on the Tramway Level of the mine. Air was released through the throttle to pistons that drove the wheels, similar to a steam engine. The locomotive was used to transport ore from the shafts across the Tramway Level and dump it into the top of the mills, where crushing, milling, and refining took place. Locomotive 9 weighed approximately 27,000 pounds and operated on 22-inch gauge track.