M-10003 to M-10006
The Union Pacific Railroad's M-10003, M-10004, M-10005, and M-10006 were four identical streamlined 2-car power car diesel-electric train sets delivered in May, June, and July 1936 from Pullman-Standard, with prime movers from the Winton Engine Corporation of General Motors and General Electric generators, control equipment and traction motors.
Union Pacific was able to maintain daily service on the Chicago-Denver run for seventeen years by dedicating three locomotive sets to that service and re-purposing power units from M-10001 and M-10004 (three total) to provide additional power and keep at least two of the locomotive sets in running condition at any given time.
These power sets had stylistic elements in common with the Illinois Central's Green Diamond unit, which was completed just previous to them.
They shared a divided front air intake grille that dominated the nose, edged in shining stainless steel.
The IC121 Diamond was a single power unit setup with a smaller articulated trainset, and in that regard had more in common with the earlier M-10001.
The copious round porthole-style windows on the power units became a "trademark" feature of Union Pacific locomotives for a number of years.
The lounge car of the M-10004 set was also built with a food preparation facility occupying its blind rear, which was revised with a new layout and porthole style rear windows between the train's City of San Francisco and City of Los Angeles service periods.
The M-10005 and M-10006 trainsets were built straight-sided to increase interior space, semi-articulated, and shorter by two sleeper cars than the M-10004 set.
Other changes included a gyrating signal light installed below the main headlight after the Second World War, the loss of the stainless steel trim on the pilot, the addition of the Chicago and North Western Railway herald to the nose in addition to the Union Pacific one, and changed nose-side badges for the route.
The demands of long-distance high speed City train service taxed the ability of the M-1000x fleet to meet them.
The original 2400 hp power sets with Winton 201A Diesel engines were underpowered for their service requirements and had a short lifespan for mechanical parts, with at best 100,000 miles between piston replacements.
