The two units were streamlined, 90 feet 10 inches (27.69 m) in length, capable of producing 2,500 horsepower (1,900 kW), and reputedly able to attain speeds of 125 miles per hour (201 km/h).

Stylistically, they resembled UP's Pullman-designed M-10003 through M-10006 power units and contemporary Electro-Motive Corporation (EMC) diesel designs.

The two locomotives were delivered to UP in April 1939, and they completed test runs and participated in a variety of publicity events for the railroad, including the grand opening of the Los Angeles Union Passenger Terminal, the world premiere of Cecil B. DeMille's film Union Pacific, and an inspection by President Franklin D. Roosevelt.

[1][2] To produce an altogether new type of locomotive, GE hoped to adapt mature steam turbine technology from maritime and stationary applications for railroad use.

The GE locomotives had lightweight bodies consisting of steel frames covered with riveted sheet metal, most of which was made of aluminum.

The two units built for UP were streamlined and capable of producing 2,500 horsepower (1,900 kW), and had been designed to operate together "elephant style", nose to tail.

[2] They were then delivered to UP in April 1939 at Omaha, Nebraska, in time for the 70th anniversary of the completion of the first transcontinental railroad in May, and given road numbers 1 and 2.

[2][5][8] According to UP historians William Kratville and Harold Ranks, the new locomotives were hoped to be the "replacement to steam" and the "successor of diesels".

[2] During test runs, the locomotives displayed excellent acceleration and an ability to maintain schedules better than conventional steam engines, although they also had serious reliability problems and relatively high maintenance costs.

[2][5][8] While UP retained interest in the concept of steam turbine locomotives for the next two years, in December 1941 it decided to end its agreement with GE.

[8][9] Rail transport author Brian Solomon opines that this was due to the development of other types of locomotives, particularly the 4-8-8-4 "Big Boy" steam locomotives, EMD E-units, and EMD FT freight diesels, as well as a potential personnel change in the railroad's motive power department in 1939.

During the "power crunch" on American railroads caused by World War II, in 1943 the steam turbine locomotives were operated by the Great Northern between Spokane and Wenatchee, Washington.