The story of the Princess Coronation Class is one of split personalities and purposes. The original streamlined form of the class arose from tests on Stanier's development of the Princess Royal class locomotives. When the opportunity to produce five conventional versions of the Coronation Pacific as a comparison to the streamlined version arose, Stanier was quoted as saying, 'They can have their streamliners if they b***** want them, but we will also build them five proper ones' such was his lack of interest in a streamlined locomotive specifically.
Those first five conventional locomotives were 6230 Duchess of Buccleuch to 6234 Duchess of Abercorn, colloquially known as Duchesses, after the first of this sub-class. Appearing in 1938 with a single chimney and without smoke deflectors, many purists regard these as the finest Pacific locomotives ever produced. The next four Duchesses to appear were 6249-6252 in 1944 and they emerged from works with a double chimney.
Originally ordered as streamlined, the demands of maintaining the streamlined form exceeded the cost savings in coal and so they emerged from works without the casing, but with streamlined tenders (which had been completed before that decision was taken). In 1946 the next three Duchesses, 6253-6255, differed in appearance again, this time the curved fall plate at the front was replaced by a split platform and smoke deflectors were fitted.
The process of de-streamlining the remaining engines began with 6235 City of Birmingham in April 1946, with 6243 City of Lancaster being the last in May 1949. Locomotives that had streamlining removed had a distinctive slant to the leading edge of the top of the smokebox, where this was previously hidden by the panels and designed to accommodate them. Eventually the raked smokeboxes were replaced with conventional smokeboxes, so that by late 1958 the majority of the fleet showed a similar appearance for the first time.