Railroads at that point were seeking a locomotive that was equally at home in yard service and on the road as these secondary operations dwindled due to abandonments. Note that the concurrent MP15 series was the last series of EMD end-cab switchers, and that they had been designed with Blomberg road trucks in place of the traditional AAR switcher trucks that were limited to 45 MPH. The MP15s had optional toilets (which at least some of the Milwaukee units had), which as oltmannd notes were required for road service in many areas.
the GP-15 was not an end cab switcher. It was a true road switcher with a short hood which had the toilet. It also used standard Bloomberg trucks. EMD found a way to minimize smoke by running the engine at 120 degrees instead off the normal 160-180 setting. Contrail bought 100 of them and they were very nice to run in the yard or on the road.
EMD used a lot of components if the railroad traded in GP-7's GP-8's or GP-9's trucks, and traction motors, air compressor, main generator and auxiliary generator were also used after rebuilding which gave the railroads a new locomotive that was shorter with a new 645 V-12 or a turbocharged 645 V-8. All Conrail engines used the naturally aspirated V-12. Modern cab eliminated water cab heating in favor of electric heat two radiant heaters one on each side and two heaters with a three speed fan for main heat and window defrostin. First one I ran was 24 days after it was delivered. It also eliminated electrical problems the first generation GP's had because the entire electrical system was -2 technology..
Conrail had one GP-8 at Beacon Park that drove the electricians nuts by after it went back into service by trippig the ground relay on the main generator took a electrician riding with me switching in the yard at night to find the problem. Under the main electrical board which held the reverser, main power contactors he saw something when it tripped for 15th time that night. Asked me to stop isolated the engine took up the floor board to access the pan thats underneath the main panel crawled into that area after I shut down the engine and came out with a
chrome metal flashlight with dozens of spot welds all over it. Someone dropped into the pan under the main panel and every now and then it would touch one of the main generator terminals from the reverser. We didn't have any more ground relay problems from then on. This is why railroad flashlights are made of rubber or plastic. The engine house foreman after that discovery stopped every road crew going out and wanted to see the engineers and firemans flashlights. He confiscated 38 of the metal flashlights in one week and gave each employee a new yellow rubberized flashlight to replace it with a box of 6 bulbs and 6 new D sized batteries.
Something for all you engineers working on short lines with older power to think about.
stay safe keep alert out there.
Never write comments when your overtired you make errors you don't see until you review your posting days later.