A number of manufacturers built diesel aero engines in the 1920s and 1930s; the best known were the Packard air-cooled radial, and the Junkers Jumo 205, which was moderately successful, but proved unsuitable for combat use in World War II. The Blohm & Voss BV 138 trimotor maritime patrol flying boat, however, was powered with the more developed Junkers Jumo 207 powerplant, and was more successful with its trio of diesel Jumo 207s conferring upwards of a maximum 2,100 km (1,300 mile) combat radius upon the nearly 300 examples of the BV 138 built during World War II.