The UP ran a competition between the three remaining domestic locomotive builders to come up with dual diesel locomotives as a unit reduction experiment. The brainchild of D. S. Neuhart, the UP's CMO (Chief Mechanical Officer), the concept was to replace as many as 10 first generation units with three dual engine units, which would develop 15,000 horsepower. By mid-1963, all three builders had designs ready, with Alco enjoying a 500 horsepower advantage, using two 16-cylinder 2750 hp Model 251C diesels, placed on the frame with the GT-598 generators facing the ends, and radiators located in the middle. Alco built three C855's, two with cabs and one B (booster), numbered 60, 60B and 61. The trucks and span bolsters came from retired gas-turbines reconitioned by the UP and shipped to Alco. The boxes on the running boards are for sand. At 86 feet in length, 16 feet 4¾ inches tall, the 5500 horsepower C855 tipped the scales at 528,000 pounds fully provisioned. The C855's spent their lives in the general freight pool based at North Platte, Nebraska. Unfortunately, they were prone to nagging failures, and with Alco's uncertain future, no more C855's were built. All three C855's were scrapped after a little over six years of service.

Number M-69 was built by Brill in 1930 as Oregon Short Line M-69 (c/n 22866-1) and retired in May 1958. It was a Brill Model 350, weighed 57 tons, was powered by a Hall Scott 300 horsepower gasoline engine driving GE electrical equipment, and seated 70 passengers. It was retired in May 1958 and presumably scrapped. Nice trailing car, sorry, I couldn't accurately read any numbers, so I am relying on the slide mount to tell the truth.

When EMD designed the cabless DD35, the intent was to use a GP35 (or any cab equipped locomotive) as the lead. There was concern about "nosing", the tendency for such a large rigid wheelbase locomotive to go straight when it encountered curves in the track, thus realigning the track. The track standards were better on the UP than some other railroads, and the problem did not materialize. So the UP asked EMD to install cabs on the next batch of 15 DD35's, and by the time of the order, EMD had some 645 prime mover equipped SD40's in field testing, so the DD35A's got the same flared radiators as the test units. UP DD35A 82 was equipped for Radio Control (RC) operation in May 1968, serving as the control unit, matching UP #82B which served as the remote. All radio control equipment was removed from both units during July 1973 at Salt Lake City, Utah.

A total of 13 out of 82 former MP B23-7's were repainted UP yellow with Missouri Pacific as the road name. This unit was not among those with MP lettering, however, it has the North Little Rock style of UP lettering, using a more squared font, most noticable in the letters U, O, and C.