In 1949, EMD introduced the SW7 switcher as the successor of the NW2. It still had the twelve-cylinder 567A engine, but now with 1,200 instead of 1,000 hp. Like its predecessor, it had two exhaust stacks on the hood. 489 were built until January 1951. 15 more were built as permanently coupled cow-calf pairs where only one locomotive had a cab.
In 1950, the SW8 was introduced as a less powerful variant with an eight-cylinder that delivered 800 hp. It could be distinguished by the single exhaust stack. 309 were built by EMD in the USA and 65 for the Canadian market were built by GMD in Canada. 41 of the locomotives built in the USA were delivered to the Army for use in the Korean War and many stayed in South Korea after the war. The cow-calf variant of the SW8 was called TR6 and twelve were built.
Two months before the completion of the last SW7, the first SW9 was built. As its direct successor, it still had 1,200 hp, but the engine was now of the more modern 567B variant. When production ended in December 1953, 786 had been produced by EMD and 29 by GMD. The TR5 cow-calf variant numbered ten pairs with two additional boosters built. Soon, this generation of switchers was replaced by the SW900 and SW1200.
