Not long ago, I noticed that Broadway Limited did a second run of N scale GE AC6000s. Most notably, I noticed that the UP units were in the post-2023 "small flag" scheme, like this photo of 6937 (BLI photo):
This came as a surprise, because I thought UP's AC6000s were out of service. But this was only partly correct. I began searching for prototype photos, and sure enough, I found some prototypes in the 6900 series in the "small flags" scheme. However, no UP AC6000s currently exist with the original 16-7HDL 6000 horsepower engines.
According to Wikipedia, "beginning in 2018, Union Pacific had begun sending its AC6000CWs to GE for rebuilding. The rebuilt units are classified as C44ACMs. By 2023, all of the units have been rebuilt."
As far as I can tell, all AC6000s, original, convertible, or rebuilt have two main spotting features. First, the right side running board jogs upward between the equipment box behind the cab and the rear truck. Second, the radiator extends out over the rear running board.
So let's recap UP's main groups of AC6000s. The Wikipedia link is the best source I've found. The original 6000 horsepower units were numbered 7500-7579, delivered between November 1995 and January 2001. As noted above, these were returned to GE for rebuilding with 4400 horsepowwer engines, but with no outward changes, starting in 2018. Going through my own photos, it looks like I never caught any in the original 7500 series -- for whatever reason, they must not have operated in Southern California.
Units 7300-7405 were "convertible", delivered with the older 4400 horsepower 7FDL engine, with the idea of upgrading them to the 6000 horsepower engine, but this never happened. These units were renumbered to 7010-7079 to make room for ES44ACs, but are not in the same order. They were classified as C4460AC and rebuilt to C44ACM later on in 2018. It looks like I never caught many of these before they were renumbered, but several afterward. But based on the dates of the photos, it's not clear when this renumbering took place. (all photos below are by me):
UP 7342 West Colton November 27, 2013
UP 7010 Cajon 1999
UP 7028 West Colton December 24, 2014
UP 7052 West Colton September 26, 2012
All the original 6000 horsepower units were returned to GE and rebuilt with 4400 horsepower GEVO engines between 2018 and 2023. They were renumbered 6888-6968. Again, based, on the dates of the photos from the metadata in the image, I'm not sure if the dates in the Wikipedia entry are entirely correct.
UP 6898 West Colton February 28, 2018
UP 6911 West Colton January 13, 2016
UP 6961 West Colton April 29, 2014
So the 2024 BLI units numbered in the 6900s with the "small flag" scheme are, strictly speaking, 4400 horsepower C44ACM locomotives, not AC6000s, but they are correctly painted, correctly numbered, and are currently in service.
