A first-flight of a prototype Bu 133 was recorded during 1935 and this form was powered by a Hirth HM506 air-cooled inline piston engine outputting 140 horsepower and driving a two-bladed propeller at the nose. The aircraft gave a good showing during testing, formal evaluations, and aerobatic displays but global customers were slow to appreciate the advanced aerobatic trainer for the market largely passed on the Bu 133A model and only a pair of Bu 133B aircraft were completed. The Bu 133C was finished with a Siemens-Bramo Sh14A air-cooled radial piston engine under a more stylish cowling and it was this variant that went on to shine on the global stage: fifty-two examples went to the Swiss Air Force from the Dornier brand label (licensed production) and another fifty or so were delivered to the Spanish Air Force by CASA (these as the CASA "1-133").
By the end of the 1930s, the Bu 133 was secured as the primary advanced aircraft trainer for the German Luftwaffe - these would be used as a critical stepping stone for up-and-coming airmen soon to serve the Luftwaffe in constant air battles all over the world. The aircraft went on in this role until the end of the war arrived in 1945. Beyond the Germans, Swiss, and Spanish users mentioned there were also global operators to be found in Axis-aligned Hungary, the Independent State of Croatia, Axis-aligned Romania, Slovakia, South Africa, and Yugoslavia. The series operated actively into the 1960s such was its excellent design while some went on to hit the civilian racing / aerobatics circuits as well for their time aloft.
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