Compressed air locomotives were used in enclosed areas such as mines, where the fumes, heat, and sparks of a steam locomotive could cause an explosion.

This one served at the Homestake Gold Mine in the Black Hills of South Dakota from 1923 until 1985. Mining began there in 1876, and they started using "fireless" compressed air locomotives in 1901. Homestake eventually had more of these than any other mine in North America. By the time it closed in 2003, Homestake was the second-largest producer of gold in the United States.

In 1985 they donated this one to the newly-formed Arizona Railway Museum, who gladly accepted it as their first donation. It was initially put on display at the Mesa Southwest Museum, and remained there until moving to the ARM's Armstrong Park location in 1997.

Compressed air locomotives were used at only one location in Arizona. The Ray Mines near Kearney had twenty of them, but they were of a larger compound design. One of those is on display in Kearney. Nevertheless, this Homestake locomotive provides a good example of a compressed air mining locomotive.

This one was built by the H. K. Porter Company of Pittsburgh in 1905, construction number 3290. It weighs 10,000 pounds, has 23-inch drivers, 6 x 10 inch cylinders, and a tractive effort of 18,600 pounds. Its track gauge is 18 inches, and it has an 0-4-0F wheel arrangement, with the F standing for "fireless." This could also be referred to as an 0-4-0CA compressed air locomotive, to distinguish it from a fireless steam locomotive.

Its storage tank contained 40 cubic feet of compressed air pressurized to 1,000 psi, significantly more than in typical steam locomotive boilers which rarely exceeded 300 psi. For this reason, these locomotives were constructed with inch-thick steel tanks held together with large rivets, giving them a unique appearance. The high pressure air was passed through a reducing valve which lowered it to about 150 psi at the cylinders.

After retiring it from service, the Homestake Mining Company donated this locomotive to the Arizona Railway Museum in 1985. In June of that year, museum members Bart Barton, Roger Netz, and Dave Harnish drove a leased flatbed trailer to Lead, South Dakota, where they were joined by members Sheldon and Stanley Schwedler. On June 23, with the help of a Homestake crew, they loaded the locomotive and over a ton of spare parts onto the trailer.

 On June 27, the Arizona Railway Museum was still under construction so the locomotive was unloaded for "temporary" display at the Mesa Southwest Museum with the assistance of a crew from Empire Machinery. It was mounted on a section of 12-pound rail that had been installed a week earlier.

Homestake No. 5 remained at the Mesa Southwest Museum until finally being moved to the Arizona Railway Museum's Armstrong Park location on June 25, 1997. It then moved with the rest of the equipment to its current location at Tumbleweed Park in 2006.

	2/27/2013 - Photo of locomotive controls.
	Photo of locomotive after repainting.
	Photo of locomotive at old ARM display yard.

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