Beginning in 1948, Union Pacific and GE developed gas-turbine alternatives for heavy freight because early diesel locomotives had relatively low power. The resulting 55 units replaced the usual diesel prime mover with an aircraft gas turbine. The last thirty turbines, UP 1-30, were the largest and most powerful internal combustion locomotives ever built at 166 feet, but they were not fuel-efficient. The lead unit carried a cab, controls, and an 850 hp diesel used to start the turbine and for low-speed movement. In the second unit, the turbine drove two main generators that supplied electricity for twelve traction motors. A tender from a retired steamer held thick bunker C fuel oil for the turbine. All turbines were retired by 1969 as new diesels were developed and fuel costs rose. UP 18 was obtained from another museum in 1992, and only two turbines survive.