A Bulgarian military mission evalutaed the B 135 and an order was placed for twelve B 135s. The Bulgarians were to licence build 50 more, and they were to be called the DAR-11 Ljastuvka (Swallow). The B 135s were delivered in mid 1941 along with the drawings, but no production was undertaken.
The B 135s were primarily used by the Fighter Pilot School. They were used in defending against USAAF bombers.