The C38 was a class of Pacifics built for the New South Wales Government Railways that became famous for its partial or complete streamlining. Designed by Harold Young, it was built to haul important express trains through the state without double-heading. They incorporated the latest advancements in steam locomotive building and were influenced by American streamliners like the Norfolk & Western class J.

They had integrally cast cylinders and frames and all axles were equipped with roller bearings. The boiler had a Belpaire firebox with five arch tubes and a grate of 47 square feet or 4.37 square metres. Other features included a power reverser, air sanders and a rocking grate. The first five were built by Clyde Engineering between December 1942 and February 1945 which were fully streamlined. 25 more partially streamlined locomotives were built by the NSWGR's own shops between 1945 and 1949, 13 at Eveleigh and 12 at Cardiff.

This was the last class of steam locomotive built in New South Wales that was built for passenger service. They could haul 450 tons over inclines of 1.33 percent and are said to have reached speeds above 80 mph. Ultimately, their power was limited by the lack of a mechanical stoker, so that initial test runs had been made with a second fireman. The last were withdrawn in 1970 and four have been preserved. The fully streamlined class leader 3801 is still in operational condition today.