The DH643 (aka C643H, C643DH) was built by Alco in 1964. Only three were made, all for Southern Pacific. The double-engine 4300-hp units were made as domestic alternatives to the Krauss-Maffei ML-4000s. They are one of those locomotives which, if you've never heard of them, will make you think "What the?" on seeing one. If you know they exist at all, you can't mistake them for anything else. The engines are massive, with a long hood with a symmetrical appearance resulting from the two prime movers. The large radiator grilles, two per side, are very prominently raised. The frame edges are negligibly thin. The fuel tank is huge and angular. There are two large air tanks per side, one above each truck. The trucks somewhat resemble standard Alco trimounts, but are positioned with the inboard axles closer, the reverse of the way other 6-axle Alcos are. http://www.rr-fallenflags.org/sp/sp9152.jpg http://espee.railfan.net/nonindex/c-643_photos/9151_sp-c643-bob_dengler.jpg http://en.wikipedia.org/wiki/Image:Southern_Pacific_-9152.jpg http://abpr2.railfan.net/abprphoto.cgi?august06/08-31-06/sp9800_kermit_geary_jr.jpg Railfan.net ABPR Archive http://home.att.net/~cz19/SP-hydr.jpg Two DH643s with a C630, showing the radical differences between the hydraulics and other Alcos.