[1] The first prototype, the B-35/1, displayed excellent flying characteristics and high speed and was originally powered by a Hispano-Suiza 12Ydrs piston engine.

The powerplant was later changed to a 12Ycrs with an identical power output, but with provision for an autocannon to be fitted between the cylinder banks to fire through the propeller hub.

A preproduction series of ten aircraft was ordered, but before these could be built, Czechoslovakia was occupied by Germany in March 1939.

The elliptical leading edges of the wings had been replaced with straight ones, and an outward-retracting main undercarriage was fitted.

With German markings and the registration D-IBPP, it was displayed at the Salon de l'Aéronautique[clarification needed] in Brussels, where enough interest was generated to spur development of an improved version of the aircraft as the B.135.