The 9000 class were used on the Union Pacific for thirty years. I am sure others might have different opinions but the Union Pacific continued to use them until very late in steam operations. They ended up on the main line and the KP line, which could handle large steam.ĭid the Challengers provide a 100% substitute, I would say no since the 4-12-2's were used until they were no longer needed. One more factor was the long wheelbase and the problems of using them in certain areas with tight radius cuves. By the time the first Challengers were built, the 9000 class had run for ten years and were already being rebuilt with disc main drivers and other upgrades to allow higher speeds for the Overland main line. The third cylinder with the associated valve gear was always a high maintenance type of design. The higher speed capability is certainly the main factor with the Challengers replacing the UP 4-12-2's, but maintenance was also a factor.
I certainly agree with your information and would like to add some addtional thoughts.
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