From Dodge Wiki
The DeSoto Diplomat was a product of the Chrysler Corporation for sale in export markets outside of the United States. DeSoto Diplomats were essentially Dodges or Plymouth Badge engineering as DeSotos and sold outside North America. They were manufactured both in Detroit, Michigan, USA, and in Windsor, Ontario, Canada.
The export DeSoto based on the Plymouth was first introduced in 1937 and was built in Detroit. Chrysler Corporation of Canada did not start building export DeSotos until late in the 1939 model year.
In 1946, the export DeSoto became the DeSoto Diplomat. They were exported to Europe, South Africa, South America, Hawaii, and Australia. In 1955, Chrysler of Canada did not export any cars and all 1955 Diplomats came from Detroit. In the late 1950s, some European taxicab drivers preferred to have a Perkins Engines P4C Diesel engine in the Diplomat; these diesel engines were installed on a Belgium assembly line.
From 1938 to 1956, the export DeSoto used Plymouth bodies with a grille that looked similar to the regular DeSoto but fit the Plymouth grille opening. From 1957 to 1959, the DeSoto Diplomat used the DeSoto Firesweep front clip with Plymouth body.
The 1960 and 1961 DeSoto Diplomats were based on the full-size Dodge Dart. Although 1960 was the last year for DeSoto in Canada and 1961 for the United States and export markets, Chrysler South Africa built a number of 1962 DeSoto Diplomats based on the Dodge Dart 440 sedan.