https://en.wikipedia.org/wiki/Avia_B-534
https://en.wikipedia.org/wiki/Avia_B-534#Operators
En Bulgarie, un royaume avant qu’il ne soit envahi par l’Allemagne fin 1944
Bulgaria bought 78 B-534s in 1939, well after the partition. The last batch of these aircraft arrived in March 1942. On 1 August 1943, seven of these aircraft were able to make two passes at American Consolidated B-24 Liberator bombers returning from the raid on Ploieşti. Hits were scored but no B-24s were shot down and some of the B-534s that received damage in the combat, cracked up on landing. After the anti-German coup of 9 September 1944, Bulgaria switched sides overnight and its B-534s were often used in ground attacks against German units. On 10 September 1944, six B-534s were involved in a brief melee with six German Bf 109s at low altitude. One B-534 was lost, but the Germans quickly broke off, wary of the low altitude and the B-534’s manoeuvrability.