ALCO DH-643

The DH-643 was a type of diesel-hydraulic road switchers built by ALCO for Southern Pacific in 1964. Internally it was also called C-643DH or Century 643 DH. Three were built after the SP had received their first ML-4000 built by Krauss-Maffei in Germany. The DH-643 was also twin-engined and also used transmissions obtained from Voith in Germany. But instead of the Maybach V16 engines, it had two V12 of the ALCO 251 series, each rated at 2,150 hp. Like its German sister, it was not recognized superior to diesel-electrics in the USA as these became more and more powerful in these years. Other reasons might have been the more complicated maintenance and the unavailability of hydraulic transmissions from domestic manufacturers. All three were retired and scrapped in 1973.