These locomotives were introduced in 1941 by the Southern Railway to a design by Oliver Bulleid. They incorporated a number of novel features including an all-steel welded boiler, chain-driven valve-gear, inside motion enclosed in an oil bath and "air-smoothed" casing.
The engines were produced by the Southern Railway to alleviate their acute shortage of express passenger locomotives although they were originally classified as mixed-traffic (suitable for passenger and freight) to circumvent wartime restrictions on the construction of passenger locomotives. The class were named after various shipping companies that called at Southampton.
Port Line and Holland-America Line were both from a second batch and were built in 1948 at Eastleigh Works by the then new British Railways.
The class performed well on the Southern Region's principle express trains. However, a number of problems with some of the novel features led to a contoversial decision in 1956 to rebuild the class on more conventional lines. During the following two years all thirty members of the class were rebuilt at Easleigh Works. The rebuilt engines were more predictable but probably less 'exciting' and successfully worked the Southern Region's principle trains until they were displaced by electrification in 1967.