The prototype, UP 50, was the first in a series built by General Electric for Union Pacific's long-haul cargo services and marketed by the Alco-GE partnership until 1953.

This was initially not a problem, because Union Pacific's turbines burned Bunker C heavy fuel oil that was less expensive than diesel.

But this highly viscous fuel is difficult to handle, with a room-temperature consistency similar to tar or molasses.

[citation needed] Soot buildup and blade erosion caused by corrosive ash plagued all of the turbines.

Before World War II, Union Pacific had been adding diesels to its roster, but none pulled road freight trains.

Union Pacific decided the best way for the turbine locomotives to realize their potential would be to put them on mainline freight trains.

The sides of the locomotive had numerous air intake louvers that could be opened and closed in varying patterns.

UP 50 was a carbody unit with a B+B-B+B wheel arrangement – four two-axle trucks, with pairs connected by span bolsters.

A steam generator would heat and liquefy the turbine's primary fuel supply (heavy Bunker C oil).

Union Pacific intended to use the turbines to replace its Big Boy steam locomotives, which were scheduled to be taken out of service.

This fuel burned cleanly and didn't foul the turbine blades as Bunker C oil did but was more difficult to transport and there were safety concerns.

Despite modifications to minimize these difficulties, the experiment was discontinued, in favor of running additional diesel locomotives with the turbines.

Continuous tractive effort was 146,000 lb (66,000 kg) with the 65-mile-per-hour (105 km/h) 74:18 gearing; in 1961 tonnage ratings were 6,740 on the 0.82% climb west from Cheyenne and 5,180 on the 1.14% east from Ogden.

to be at 6,000-foot (1,800 m) altitude and 90 °F (32 °C), and in cooler, denser air the turbine itself could exceed 10,000 hp (7,500 kW) if the electrical system could handle it.

[citation needed] Trains magazine mentions that the turbines' four-month trial to Los Angeles in 1962 ended when "tender wheels were motorized, imposing speed restriction".

They had Leslie S-5T-RF air horns on the cab roof (later moved to the mid radiator section of the A unit, in response to ice build-up in the bells).

Bunker C's cost advantage waned as the plastics industry began to find uses for it and improved cracking techniques allowed the oil, previously considered waste, to be converted to lighter fuel grades.

Several of the tenders were retained and converted to hold water for maintenance of way purposes and later to be used for Union Pacific's operating steam locomotives: UP 844 and UP 4014.

UP 18's tender UP 907853, built in 1937, had a long history; first built for use with UP's FEF series steam locomotives before conversion to turbine use, it served as a water tender from the 1970s to 1984 for trains such as the Expo '74 and the American Freedom Train before being donated to the Kansas Railroad Museum, and then acquired by the IRM.

[12] In October 1962, Union Pacific constructed an experimental GTEL of its own, using a modified ALCO PA-1 as a cab, the chassis of a GN W-1-class electric locomotive (bought for scrap from the Great Northern Railway) as the second unit, a modified turbine prime mover removed from one of the 50 to 75 series locomotives, and a tender salvaged from one of its own “Challengers”.

[13] The blade erosion and soot build-up problems encountered in the earlier locomotives were magnified with the coal turbine.