Locomotive Number 35 was purchased in April 1931 from the H.K. Porter Company of Pittsburgh, Pennsylvania. It served on the Homestake Tramway, hauling ore from the Homestake shafts to the Homestake mills. The locomotive was powered by compressed air, with a large air tank capacity of approximately 70 cubic feet of air at 1000 psi. It was filled from a large stationary air compressor on the Tramway, and the air was released through the throttle to pistons that drove the wheels, similar to a steam engine. Compressed air locomotives were later replaced by battery locomotives or, in some cases, electric locomotives.