The Avia B.135 was built by Czechoslovakia and 12 aircraft entered service with the Bulgarian Air Force in WW2. Additional engines and airframes were available but never used, as the Bulgarians were encouraged to buy the Messerschmitt 109 instead. Engine problems caused the aircraft to be relegated to training duty for the most part, but it did see combat in 1944 when four B.125s intercepted USAF bombers in Bulgarian air space.

The B.135 was armed with 2 7.92mm machine guns and 1 x 20mm cannon.

This example is an B.135 of the Bulgarian Air Force, circa 1944.