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.