In 1904, William Riley McKeen, once the superintendent in charge of vehicle procurement for the Union Pacific, had the idea of a gas-powered, streamlined railcar. Inspired by shipbuilding, he designed a shape that was tapered at the front and rounded at the back. Prompted by the then CEO of UP, the McKeen Company was founded to put this idea into practice. It was hoped that the petrol-powered railcars would be cheaper to operate than steam locomotives and the high acquisition costs and operational limitations of a battery railcar were to be avoided. The first, still two-axle vehicle was completed in 1905 and this was soon followed by a series of four-axle vehicles, which were ordered in large numbers by many operators in the USA.

The body was offered in two lengths of 55 and 70 feet and the interior could be fitted with either a large or small mail and luggage compartment or complete with passenger seats and a smoker's compartment at the rear with panoramic views. The windows were shaped like portholes and thus adapted to the ship-shaped car body. The engine also came from shipbuilding and stood directly on the front bogie. Only one axle was powered via the mechanical power transmission, which in combination with the low torque of the engine made for poor starting performance. From the eighth vehicle, a self-developed engine was installed, which now had 200 or 310 instead of 100 hp. There was no gearbox with reverse gear to change direction, but the camshaft could be shifted like on ships. This made it possible to run the engine in reverse after it had been stopped.

Side view of the 70 feet variant

Railway and Locomotive Engineering, September 1909

A total of 152 vehicles were built, of which 32 went to the Union Pacific and 31 to the Southern Pacific. From 1910 they also were exported. Two units went to Australia to the Victorian Railways and were delivered with a gauge of 5 ft 3 in. Five units were also delivered to the Queensland Railways with a gauge of 3 ft 6 in. Over time it became apparent that mounting the engine on the bogie was becoming a problem for the railcars. Since this was nearly unsprung, all impacts took their toll over time and made more and more vehicles inoperable. As a result, production ceased in 1917 and the Union Pacific dissolved the McKeen Company. Many railcars were later converted to passenger coaches and by the end of the 1930s there were almost no longer any engines on the road. The only example still running today belongs to the Virginia and Truckee Railroad and uses a modern drive train.

At a time when steam railcars were in vogue, the Pittsburgh, Cincinnati, Chicago & St. Louis Railroad acquired such a vehicle. Their number 2 had five axles in total and its front part was theoretically a 2-4-0 locomotive with a four-cylinder Vauclain compound engine. Its exhaust was passed to the rear of the car and used to heat the passenger compartment.

Behind the boiler and the cab, there was an additional baggage compartment. The passenger compartment, carried on the rear truck, had space for 40 persons. Since the railcar had enough power, it could also haul up to two passenger or mail cars. When running solo, it was able to reach speeds of up to 60 mph or 97 km/h. Ultimately, it shared the fate of many other steam railcars and didn't become a great success when it got superseded by gas and diesel railcars.