In 1955, Union Pacific ordered a new turbine-electric, the world's most powerful locomotive. Each would be two units plus a fuel tender, rated at 8,500 horsepower (6,300 kW).

The A unit contained the control cab and an auxiliary diesel engine generator. The B unit carried the turbine and main generators to provide electricity to the traction motors on both the A and B units. The turbine was a new design GE Frame 5 simple cycle gas turbine with a sixteen-stage compressor, ten combustion chambers and a two-stage turbine. No steam generator was needed to heat and liquify the heavy Bunker C fuel because the tenders were insulated. The original plan was to number these units in the 7000 series but they were numbered 1 to 30.

They were delivered to Union Pacific between August 1958 and June 1961. These units were very different from the previous generations, having a wheel arrangement of C-C on each of their units (not including their tenders). The locomotive weighed about 610 tons with a full tender. Continuous tractive effort was 146,000 lb (66,000 kg) with the 65 miles per hour (105 km/h) 74:18 gearing; in 1961 tonnage ratings were 6740 on the 0.82% climb west from Cheyenne and 5180 on the 1.14% east from Ogden.

With 8,500 hp (6,300 kW) from a single prime mover these engines set a record that still stands. That rating was claimed[by whom?] 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. Trains says "The big 8500 h.p. jobs remain under constant scrutiny as UP: (1) jacks some of them up to 10,000 h.p. ratings; (2) considers motorizing their fuel tenders with traction motors..."[7] Lee's book explains that UP tried resetting generator excitation to absorb the higher rating but only on test.[citation needed] The motorized tender sounds unlikely,[speculation?] though Trains mentions that the turbines' four-month trial to Los Angeles in 1962 ended when "tender wheels were motorized, imposing speed restriction."[8] (The 1961 and 1963 timetables show a 65 mph (105 km/h) limit for all the turbines.)

These turbines eventually displaced units 51 to 75. There had been problems with fuel filters clogging on the earlier turbines, so it was decided to filter the fuel before filling the locomotive fuel tanks and the tender.

Unlike the earlier turbines, the 8,500 hp (6,300 kW) turbines came with 24,000 US gal (91,000 l) fuel tenders, in addition to the 2,500 US gal (9,500 l) of diesel fuel in the locomotive tank. 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).

The turbines in these units are the most powerful prime movers ever installed in any North American locomotives.

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Scale Trains Comparison Chart