The ALCO RS-3m is a diesel-electric locomotive rebuilt from an ALCO RS-3 road switcher. These 98 locomotives were rebuilt to replace their original ALCO prime mover with the more reliable EMD 567B engine and fan assemblies taken from retired E8s. Many of these rebuilds were performed by the ex NYC DeWitt shop with 56 completed at the ex PRR Juniata shop. The RS3m rebuild program started in 1972 and continued until 1978 under Conrail. Perhaps one of the earliest examples of the RS3m is the former Missouri-Kansas-Texas Railroad's RS3m fleet. Built in the early 1950s by ALCO, the Katy had them rebuilt in the late 1950s by ALCO competitor, EMD, who rebuilt them with GP9 long hoods to make room for the larger EMD 567 prime movers. The Chicago and North Western Railway had a pair of RS-3ms (1613 & 1624) that were rebuilt by ALCO in March 1960 using an 1,800 hp 12 cylinder ALCO 251-B engine and schedule 26L air brake components. These featured long hoods from ALCO RS-11 road switchers. Missouri Pacific GP12 The Missouri Pacific Railroad had a fleet of RS-2s and RS-3s that were rebuilt in their North Little Rock shops, receiving the GP12 designation after rebuilding with EMD 567 engines. These look like normal ALCo RS-3s with the addition of more exhaust stacks. New Haven - Alco rebuilds By the year 1958 the New Haven RR needed renewed power but couldn't afford new. They decided to rebuild the RS-3 fleet "in kind" as they were ten years old by that point. And for first generation diesels, ten years was considered middle aged. Twenty one rebuilds were done by Alco in three groups. All the Alco rebuilds had the black cab/orange hood paint scheme and were able to Multiple Unit aka MU with later engines. Nose MU was added as well. These rebuilds kept the original Alco 244 engines. The New Haven didn't have the problems that other roads did with their 244 engined locos. In fact, the RS-3's were considered by most NH men to be the best locos they ever had. The first rebuilds: Type I — kept their steam generator, and single bulb reflector headlights; #526 & #529 kept their buffer plates for diaphragms. #518, 526, 529, 549, & 553 were rebuilt May 1958 - June 1958. Type II — kept the steam generator but got twin sealed beam headlights. #533, 551,