In the summer of 1939 the Bulgarian Air Force bought from the Wirschaftsgruppe Luftfahrtindustrie in Berlin, 78 of the B-534s of the 4th version. These were delivered by train to Karlovo and issued to the 2nd istrebitelen orlyak (2nd Fighter Air Regiment). Each of its four combat yatos (Squadrons) got 15 of the B-534s, the training yato receiving a dozen of them. These units were located at the Karlovo and Vrazhdebna (near Sofia) airfields.

2nd orlyak was sent to Bozuriste when the Serbian’s bombers made attacks on Kjustendil, west of Sofia.

In March 1942 the 6th istrebitelen orlyak (6th Fighter Air Regiment) received its B-534s, allotting them to the 612th yato, based at the Vrazhdebna airfield, and to the 622nd yato, based at the Bozhurishte airfield, near Sofia. 6th istrebitelen orlyak was a mixed unit equipped with Bf 109s and B-534s.

On 1 August 1943, the B-534s took off for the biggest fighter operation in which this type was to take part when Avias were sent against the American B-24 Liberator bombers that took part in the raid on the Romanian oil refineries at Ploiesti.
At 12.25 six B-534s of 612th yato took off from the Vrazhdebna airfield. At the same time another 4 planes of the same type from 622nd yato took off from the Bozhurishte airfield. Also at the same time took 10 Bulgarian Bf 109G-2 of 6th istrebitelen orlyak off from Karlovo. Of all these aircraft only the aircraft flown by podporuchyks Vaptzarov and Daskalov (flying Avias) made visual contact, seeing the bombers far away to the north, over the Danube River.
At 15.00 the American bombers started to return, some of them damaged and low on fuel and the Bulgarian fighters took to the air again. Four B-534s took off from Bozhurishte and seven from Vrazhdebna. Four Bf 109s from Karlovo, led by porutzyk Stoyan Stoyanov, also took part in this interception. The Avias climbed as high as possible and started to see small groups of Liberators, coming form the north. The combat started between the towns of Vratza and Ferdinand (now Montana) at 3.000 metres. The seven Avias from Vrazhdebna dived towards a large group the bombers. They dived with high speed firing all their machineguns and passed between the enemy formation continuing almost to the ground before starting all over again. Getting to the bombers was a hard work and took a long time since the fighter’s speed was just a little higher than the bomber’s. Despite this, near the town of Kjustenil, the Avias made a second attack. Despite the heavy fire from the "Liberators", the Bulgarian Avias made two good attacks against the enemy. In both there were many successful hits, but the small calibre machineguns could not do much against the well-armoured American bombers and what is more, a number of Avias was destroyed during landings.

© Jerry Boucher.
Picture kindly provided by Jerry Boucher from the VIRTUAL AIRCRAFT WEBSITE.
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It was perfectly clear that for any further fighter career the Avia B-534 was hopelessly obsolete. The surviving machines were thus transferred to the 2. shturmovy orlyak (2nd ground-attack Air Regiment), which used them to equip its 2nd yato (2nd Squadron). As of 30 August 1944 it had some 19 ‘Dogans’ (Hunting eagle or hawk), as the Bulgarians called their B-534’s, with 10 of them airworthy.

In June and August 1944 the Allies in bombing raids on the Bulgarian airfields destroyed many of the Avias.
One Avia was destroyed in fights against Communist partisans while more were lost in accidents.

On 9 September 1944 there was a anti-Nazi coup in Bulgaria and their erstwhile ally all of a sudden become the enemy.

During the fights against the Germans the 2/2 shturmovy orlyak flew 71 missions and 140 sorties of approximately 250 hours between 10 September 12 November 1944. They claimed 22 artillery guns, 52 motor vehicles, 4 tanks, 62 horse-cars, 1 military train and one railway-stop using their machineguns and small bombs. They also flew many reconnaissance sorties allowing the Bulgarian Ju 87s to attack with efficiency.

At 06.40 on 10 September 1944 six German Bf 109s intercepted six Bulgarian Avias over the railway-stop at Verinsko. The Bf 109s attacked and the B-534s tried to answer this but it was a short affair since the Messerschmitts didn’t want to get involved in a dogfight with the much more manoeuvrable Avias at low height so they left after the first bounce. They had however shot down Avia B-534 no. 26 but fortunately the pilot Vesselinov survived.

On 15 September Avia B-534 no. 63 were shot down by anti-aircraft fire over Tzurkvitza, near Kjustendil, the pilot however bailed out.

On 18 September Avia B-534 no. 19 were hit by anti-aircraft fire but managed to land and was later repaired.

On 24 September Avia B-534 no. 58 were hit by anti-aircraft fire but the pilot managed to return to Vrazhdebna and the aircraft was later repaired.

Reportedly the 2nd ground-attack Regiment had 6 combat worthy Avias on its strength as late as on 1 January 1945, when it was operating in Hungary. In the autumn of 1944 several B-534’s reappeared on strength of the 2nd Fighter Regiment, where their career ended as late as in summer 1945.

Source:
Avia B-534 - Jirí Vraný, 1994 MBI, Praha, ISBN 80-901263-6-7
Additional information kindly provided by Theodor Muchowski