Instead of being an opponent of the German Bf-109 this sleek fighter became its ally.
The Avia B.35 was a fighter aircraft built in Czechoslovakia shortly before World War II. It was designed to meet a 1935 requirement by the Czechoslovakian Air Force for a replacement for their B-534 fighter biplanes. The B.35 was an elegant, low-wing monoplane with an elliptical wing. The fuselage was constructed from welded steel tube, covered in metal ahead of the cockpit and fabric aft, while the wing was of entirely wooden construction. Rather anachronistically, the Air Force specified a fixed tailwheel undercarriage for the aircraft, in the hope that this would speed development, as the mechanism for retracting the undercarriage was simply not yet available.
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. Testing continued until 22 November 1938, when the aircraft was destroyed in a crash that killed Avia test pilot Arnošt Kavalec. Nevertheless, a second prototype, B-35/2, was already reaching completion, and was fitted with redesigned ailerons and flaps. It first flew on 30 December with testing beginning in earnest in February 1939. A pre-production series of ten aircraft was ordered, but before these could be built, Czechoslovakia was occupied by Germany in March 1939.
Development however was resumed under German control, with the substantially revised B.35/3 flying in August 1939. The elliptical leading edges of the wings had been replaced with straight ones, and an outwardly-retracting main undercarriage was fitted. This prototype was the first to actually carry its intended armament. Now, wearing German markings and the registration D-IPBB, it was displayed at the Salon de l'Aéronautique in Brussels, where enough interest was generated to spur development of an improved version of the aircraft as the B.135.
The B.135/1 prototype attracted the attention of Bulgarian Air Force officers visiting the Avia plant, and a production contract for 12 aircraft and 62 engines was signed, as well as a license to allow an additional 50 airframes to be constructed by DAR as the DAR 11 Lyastovitsa (Bulgarian: "Лястовица"; "Swallow"). However, the DAR facilities proved to be incapable of producing the aircraft, and only the 12 Czech-built examples were ever made. Plans for further production were stopped by the RLM, which also interrupted engine deliveries after 35 units, and the Bulgarian Air Force was encouraged to purchase the Messerschmitt Bf 109 instead.
In service, the B-135s gave continual engine problems and were soon relegated to training roles. Four aircraft did, however, see combat on 30 March 1944 when they intercepted USAAF bomber formations encroaching on Bulgarian airspace after attacking Ploieşti. Some (Bulgarian) sources credit Lieutenant Yordan Ferdinandov with a B-24 Liberator kill that morning. According to Bílý all four Avias, led by Captain Atanasov, took part in the possible shooting down of a 4-engined bomber that day. The downed aircraft crashed in the area of Tran and Breznik according to the log of Lieutenant Yordan Ferdinandov.