The SD9 was produced from 1954 to 1959. It had a 16-cylinder engine that put out 1,750 horsepower. These locomotives rode so smoothly the engineers gave them the nickname “Cadillacs”.
The Northern Pacific never owned any SD9s, neither did the SP&S, but the Great Northern owned 27, the CB&Q had 80. The Burlington Northern Railroad rostered 135 from the merger. Southern Pacific had 150; about 50 of them had steam generators for use in passenger service. The Milwaukee Road had 14, when they were rebuilt they became SD10s.
After the SD9 ended production, the SD18 took over, then the SD24 went into production. The SD18 was 1800 hp, none of the railroad here in the Northwest ordered any SD18s. The SD24 was a 2400 hp locomotive with a turbocharged engine; the CB&Q and Union Pacific purchased the SD24.