Avia B-71 in service with Bulgaria

 

The Avia B-71 was a license-built Czechoslovak variant of the Tupolev SB. This variant saw service with Bulgaria.

In September 1939 Bulgaria bought 32 B-71 from Germany. Those machines were originally built at the GAZ 22 factory, in Fili, Moscow oblast, and were delivered to the Ceskoslovenské letecvo (CL - Czechoslovak Air Force) in March 1939, just before the German Occupation.

The Germans handed the B-71s to the Vazdushni Voyski (VV - Royal Bulgarian Air Force) at Merseburg, Germany and were not operational until early 1940, when they were assigned to the 5. Bombardirovochen Polk (5.BP - 5th Bomber Regiment), based at Plovdiv. The B-71 received the nickname of "Zherav" (crane) from Bulgarian pilots.

The Bulgarian B-71s saw combat for the first time in late September and early October 1941 when Greeks in the Bulgarian-occupied region of Thrace revolted. Three B-71s took off from Plovdiv and bombed the Greek town of Drama, in north-western Macedonia. This turned to be the only combat mission of the 5.BP during the period that Bulgaria was allied with Germany.

On 5th September 1944 the USSR declared war on Bulgaria (which, until then, had remained neutral in the Axis war against the USSR) and the Soviet Army invaded three days later. During this period, the pro-Soviet Bulgarian faction called "Democratic Party of the Patriotic Front" led by Kimon Georgiev, seized power and declared war on Germany on 9th September. 

In November 1944, the 2. Yato (Squadron) of the 5.BP had a total of 21 B-71 on strength. On 14th November the 5.BP was redeployed from Plovdiv to Vrazhdebna, close to Sofia, from where they took part in various bombing missions against the retreating Wehrmacht. On these missions, the B-71s had not a precise targets, but where instructed to take upon targets of opportunity in certain pre-defined areas where the VV thought German troops were concentrated. 

The Bulgarian B-71s were heavily employed over Yugoslavia. On 18th November three B-71s attacked a German train at the Vuchitran train station, causing heavy damage to the train. The next day four B-71s bombed the Zhitarica railroad station. Although they were meet with heavy anti-air fire, they returned safely to Vrazhdebna. 

Two days later, on 20th November, several B-71s flew a 'free hunting' mission against targets of opportunity in the regions of Mitrovica and Rashka, attacking a train north of Mitrovica at 12:30 hours. In this bomb run Zherav 4's bomb bay doors malfunctioned and couldn't release its bombs and Zherav 11, flew by Sgt. Manol Dojchev became disoriented and had to force-land at Staro Zhelezare, close to Plovdiv. 

The fourth and final bombing mission of the Bulgarian B-71s took place the next day, on 21st November when four B-71s joined a formation of approximately 15 Lockheed P-38 of the US 15th Air Force. The B-71s bombed a motorized German column near Kamenica while the P-38s attacked a railroad station near Mitrovica. This constituted the only joint Bulgarian-American action against Germany during World War 2. During this action Zherav 4 lost its bearings and had to force-land at Shtarklevei.

After this attack the front moved beyond the range of the B-71s. During their service period with Bulgaria, they made a total of 14 sorties during those four missions in which they destroyed a total of two railroad stations, three trains and one German motorized column, at the cost of no Bulgarian airman killed or wounded.

Sources:

1st Signal Squadron - Aircraft In action 194 - Tupolev SB in Action

2nd https://en.wikipedia.org/wiki/Tupolev_SB

3rd https://massimotessitori.altervista.org/sovietwarplanes/pages/sb/tapani/b-71/bulgarian/bulgarian.htm

Kaproni Bulgarski KB-11 Fazan

 

The Kaproni-Bulgarski Kb-11 'Fazan' (Bulgarian word for 'pheasant') was a Bulgarian army liaison aircraft built by Kaproni-Bulgarski, a Bulgarian subsidiary of the Italian Caproni.

Its origins can be traced back to 1938 when the Royal Bulgarian Air Force (RBAF) issued a specification for a light divisional reconnaissance aircraft with some ground attack capabilities, built around the Alfa-Romeo 126 R.C.34  radial engine, rated at 770 hp of power for take off. Kaproni-Bulgarski, led by engineer Carlo Caligaris, presented a project for a biplane, the KB-11, which was rejected as the RBAF considered the type as obsolete. Therefore, Caligaris and his team presented a second project, this time a high-wing monoplane with a fixed landing gear. A scale model of this second design was tested at a wind tunnel in Milan (Italy), where Caproni's headquarters were located and after some satisfactory results, a first prototype was built.

 

This first prototype, nicknamed as "Quasimodo", after the hunchback of Notre-Dame, was flight-tested during April 1940 by Col. Vasil Valkov and Lt.Col.Eng. Petko Popganchev who considered the type as unstable, nose-heavy in level flight and unsafe during forced landings, so the RBAF couldn't accept the KB-11 due to its many flaws.

This left Kaproni-Bulgarski in a difficult situation, as their rival company, DAR, was pushing forward with the better-looking DAR-10A. So, fearing that DAR would win the contract, they hastily redesigned the KB-11 with a high-wing supported by V-shaped struts, a revised undercarriage, a new glazed cockpit, equipped with photo-hatches, walkie-talkies and aerial cameras, and was powered by the same Alfa-Romeo engine the prototype was powered with. This redesign, was accepted by the RBAF and the aircraft was put into green light for mass production under the denomination of KB-11A. Initial operational flights made in early 1941, found that the Fazan was seriously underpowered so a new, more powerful engine was needed. 

Before the outbreak of World War 2, Bulgaria signed a contract with Poland for license production of the PZL.37 bomber, so a number of Polish-built Bristol Pegasus XX engines were supplied. However, the German invasion thwarted this operation and the engines were stored. They were found to be very handy for the KB-11A and so the PZL Pegasus were fitted to the 2nd and 3rd batches, which were characterized for driving a two-bladed propeller. 

Both KB-11 and KB-11A were armed with two 7,92 mm M-30 machine guns placed in the forward part of the fuselage plus two twin 7.7 mm FK-33 defensive machine guns placed at the observer's post. At the central part of the lower fuselage, the Fazan had also provision for eight 50 Kg (110 lb) bombs or four 100 Kg (220 lb) bombs. 

The KB-11 was initially intended to replace both the Czechoslovak Letov S.328 and the Polish PZL.43 in the short-range reconnaissance squadrons of the RBAF. The KB-11A saw action for the first time in joint Bulgarian-German-Italian anti-partisan operations against Tito's partisans in Serbia during 1943, as a ground attack aircraft. Following Bulgarian armistice in 1944 and their switching of sides, the Fazan was used to support Bulgarian ground troops in Macedonia and Serbia, serving mostly with 333rd and 453rd close recon squadrons. However, due to the resemblance of the type with the German Henschel Hs.126 recon aircraft (which also harassed positions of the Bulgarian Army), the KB-11A was sometimes victim of friendly fire who miss-identified the Fazan. That's why the KB-11A's usage during this later-period of the war was very limited and was eventually withdrawn from active combat duty. 

After the war, in 1947, Bulgaria transferred many of their former aircraft to Yugoslavia as war reparations, among them 30 KB-11A, which were used as liaison, target tug and trainer aircraft, having their wooden wings replaced with metal ones by Ikarus allowing the KB-11A to remain in active service with Yugoslavia until 1958, although some sources claim it was until 1956. 

Sources:

1st https://en.wikipedia.org/wiki/Kaproni_Bulgarski_KB-11_Fazan

2nd http://www.airwar.ru/enc/spyww2/kb11.html (translated)

3rd https://www.valka.cz/BGR-SFKB-KB-11-Fazan-t57179

SFKB Kb-3/4/5 Chuchuliga

 

The SFKB Kb-3 was a Bulgarian biplane two-seater trainer that was built in 1937. It was designed by engineer Lazarov who also designed the previous Kb-2 and incorporated various improvements into the Kb-3 on the basis of flight tests. It was nicknamed as "Chuchuliga I" (Bulgarian word for Skylark) and only 20 were completed in 1937. 

It was powered by a single Walter-Castor II radial engine driving a two-bladed propeller. Wing system was identical to that of the Kb-2A, but hull chassis and tail section underwent significative changes to improve overall aerodynamics. 

It had a crew of two and served with the Royal Bulgarian Air Force as trainer until 1944. 

The SFKB Kb-4 was a development of the Kb-3 based around various improvements. Engineer Lazarov left Kaproni-Kazanlak (manufacturers of the type) for DAR-Bozurishte in 1938 so Kaproni-Kazanlak designed an improved variant of the Kb-3 called Kb-4 "Chuchuliga II". This was powered by an American Wright E1P-975 radial engine rated at 220 hp of power , covered in a Townend ring, driving a two-bladed propeller. The Wright engine turned to be very appreciated by the Bulgarians, however, when Bulgaria declared war on the United States, their supply was cut, so some of them were completed with the Czechoslovak Walter-Castor II. A total of 28 Chuchuliga II machines were completed.

The Chuchuliga II was the first in the series to feature defensive armament as it was equipped with a 7,7 mm FK-33 machine gun which was the Bulgarian copy of the British Vickers F machine gun. 

It served with the Royal Bulgarian Air Force in the trainer, liaison and reconnaissance roles until 1944.

The Kb-5 Chuchuliga III, was a further development of the type made in 1939. The first prototype was powered by the Walter-Castor II engine, covered in a NACA cowling, however, flight testing was not satisfactory so it was refitted with an Italian Piaggio R.VII C1 engine, driving a three-bladed propeller, achieving the desired performance rates, so it was decided to put it into production. A total of 45 machines of this type were manufactured (making a total of 93 Chuchuligas of every type), however, the production version of the Kb-5 differed from the modified prototype in being powered by a single Walter-Pollux engine rated at 444 hp of power, fitted in a Townend ring and driving a two-bladed propeller. 
The Chuchuliga III featured increased fuel capacity and was fitted with radio and photographic equipment. It was armed with a single 7.7 mm FK-33 machine gun mounted in the nose, synchronised to fire through the propeller. It was equipped with a second FK-33 placed in the observer's position and could carry up to 200 kg (441 lb) of underwing bombs, 100 kg (220 lb) under each lower wing. 

The Kb-5 was the most used variant of the Chuchuliga, as it served with 113, 123, 453 and 463 reconnaissance squadrons of the Royal Bulgarian Air Force. Three aircraft also served with the 5th Bomber Regiment, stationed at Plovdiv, equipped with the Dornier Do-17M and the Avia B-71. Some few machines were also employed in the liaison role by the Naval Squadron at Varna, equipped with the Arado Ar.196 and the Heinkel He.60. 

When the USSR entered Bulgaria, they were employed actively in combat and the type was kept in active as a trainer until the early 1950s.

 

Sources:

1st http://www.airwar.ru/enc/other2/kb3.html (translated)

2nd http://www.airwar.ru/enc/spyww2/kb4.html (translated)

3rd http://www.airwar.ru/enc/spyww2/kb5.html (translated)

4th https://www.armedconflicts.com/SFKB-KB-5-Chuchuliga-SFKB-KB-5-Chuchuliga-III-t167476

5th https://www.nevingtonwarmuseum.com/sfkb-kb-4.html

6th https://en.wikipedia.org/wiki/Caproni_Ca.113

DAR-10. The Bulgarian Snipe.

 

The DAR-10 (acronym standing for Darzhavna Aeroplanna Rabotilnitsa - State Airplane Workshop) was a Bulgarian light-bomber and reconnaissance airplane which was designed by Zvetan Lazarov in 1938 at DAR's factory in Bozhuriste, near the Bulgarian capital city, Sofia. 

The DAR-10 was a two-seat (pilot and gunner) low-wing cantilever monoplane of traditional layout. It had a fixed undercarriage with spatted main wheels. Wings were made out of wood and covered in plywood and the type had no flaps.

The fuselage, constructed of steel-tube framework and wood formers was covered in fabric and, in comparison with other aircraft of the time, wide and deep to fit the Italian Alfa-Romeo 126 RC.34 radial engine which yielded 950 hp of power, driving a three-bladed propeller.

Two prototypes were built, the first of which, named DAR-10A (the A stands for Alfa-Romeo) "Bekas" (Snipe) flew for the first time on 2nd July 1941. It was designed to be armed with two forward-firing machine guns and two additional ones placed at the end of the canopy, manned by the gunner. It had provision for a total of five 100 Kg (110 lb) underwing bombs and it was also envisioned the installation of an additional 20 mm forward-firing cannon in the forward fuselage. However, it's doubtful if the DAR-10A received any armament at all.

This first prototype crashed in October 1942. Albeit having good flight reviews, it wasn't chosen for production as the high-wing Kaproni Bulgarski KB-11 "Fazan" (Pheasant) was selected instead.

The second prototype, DAR-10F (F stands for its Fiat engine) was powered by a Fiat A74 RC.38 radial engine yielding 870 hp of power. It wasn't until March 1945 that this airplane flew for the first time. It was slightly heavier than the DAR-10A and had a top speed of 454 km/h (282 mph). Owing to a stronger construction and dive brakes, it could also perform as a dive bomber. Its armament layout was the same as the DAR-10A but in this case with two additional 20 mm forward-firing fuselage cannons mounted in the upper half of the forward fuselage, on the engine. It had also provision for one 500 kg (1.100 lb) or one 250 kg (551 lb) bombs under the fuselage and four 100 kg (110 lb) of smaller underwing bombs. 

It wasn't however selected for production as the DAR-10A was discarded in favor of the KB-11 and the German Junkers Ju.87 Stuka, and the DAR-10F arrived too late, when the World War 2 was almost over, and Bulgaria had access to Soviet aircraft such as the Ilyushin Il-2 or the Ilyushin Il-10, among others.

Sources: 

1st: https://en.wikipedia.org/wiki/DAR_10

2nd http://airwar.ru/enc/aww2/dar10.html (translated)

3rd http://airwar.ru/enc/aww2/dar10f.html (translated)

Kaproni-Bulgarski Kb-6 'Papagal'

 

In 1939, Kaproni-Bulgarski factory, located at the town of Kazanlak, began to design a licensed variant of the Italian Caproni Ca.309 'Ghibili' (Italian word for 'desert wind') for the Royal Bulgarian Air Force (RBAF). 

This variant received many changes, when compared to the original Italian design and received the denomination of Kb-6 (although it was commonly known as the KB-309) and the nickname of 'Papagal' (Bulgarian word for 'Parrot'). At request of the RBAF it was built as a light transport aircraft, without defensive machine gun arrangement, but retaining bombing and photographic capabilities.

Bomb aim equipment was placed in the nose, which was enlengthened and the tail section was also changed. In the original Italian version, if the tail wheel strut broke, or if its tire burst, the tail could hit the ground damaging seriously the fuselage. Therefore, in the Bulgarian version, the tail was curtailed. Landing gear was also changed, in the Ca.309 it was completely covered, at least in the initial versions, while in the Papagal, it was completely open. This was done because of the harsh winter and autumn conditions present in the unpaved Bulgarian airfields. The main cabin, placed just behind the cockpit, was well glazed with provision to fit passenger seats or radio equipment. Some few of them were used for airborne radio operator training, with up to 4 trainees. It was powered by two German 240 hp Argus As.10C engines, instead of the original Alfa-Romeo ones.

It was officially adopted by the RBAF in 1940, when the prototype was accepted by the RBAF for testing on 28th November 1940 with a mild reception among Bulgarian pilots. The main handicap was a long instability when taking off and flying. However, it once known how to handle it, turned out to be a reliable and unpretentious aircraft, which could serve as a light transport, communications and trainer and was active until 1946. 

A total of just 24 Papagals were manufactured at Kaproni-Bulgarski's Kazanlak factory in 1941, except for the prototype which was completed in late 1940.

Sources:

1. http://www.airwar.ru/enc/spyww2/kb6.html (translated)

2. http://www.aeroflight.co.uk/waf/bulgaria/af/types/kb.htm

3. https://en.wikipedia.org/wiki/Caproni_Ca.309

Arado Ar.96, Bulgarian users

 

The Arado Ar.96 was a German single-engined, low-wing monoplane made entirely out of metal which was produced by Arado Flugzeugwerke which was exported to various countries and also produced abroad.

The Royal Bulgarian Air Force bought twenty-four Arado Ar.96B-2 (though some sources claim it was a total of thirty-four - 3 Ar.96A and 31 Ar.96B) which were delivered in May 1940. They received the nickname of "Sokya" (Bulgarian word for jay - the bird- ) and were assigned to the Royal Bulgarian Fighter School for the advanced pilot training course. 

Among those 24 Ar.96 some of the were of the Ar.96B/MG category which featured a single defensive 7.92 mm MG 17 machine gun in the rear. 

The Ar.96 served throughout all the war as the main trainer of the Royal Bulgarian Air Force with many additional one being captured as war prizes in Yugoslavia when Bulgaria switched sides in September 1944. Many other ones were captured in July 1945, just after the war, when Bulgarian troops left Austria. After the war, when Bulgaria became a communist country, the Ar.96 was still the main trainer serving with the 3rd (Advanced Training) Squadron at Telish, in Pleven, Bulgaria. Under this unit they received nine additional Avia-made machines, the Avia C.2 and they served as the main advanced trainer of both Royal Bulgarian Air Force, Bulgarian Air Army and Bulgarian People's Army Air Force until 1953 when they were replaced by Soviet types like the Yakovlev Yak-11 or the Yakovlev Yak-18.

Sources:

1. https://en.wikipedia.org/wiki/Arado_Ar_96

2. http://www.aeroflight.co.uk/waf/bulgaria/af/types/arado.htm

3. https://www.valka.cz/Arado-Ar-96-B-t6478

4. https://en.wikipedia.org/wiki/List_of_former_Bulgarian_military_aircraft

Messerschmitt Bf.108, part one

The Messerschmitt Bf.108 was a German single-engine sport and touring aircraft that was used for military liaison purposes during the World War 2. It was designed and developed by the Bayerische Flugzeugwerke in the 1930s and was exported to many countries:

• Austria: A single Bf.108 was ordered by the Austrian government on 22nd April 1937 and was delivered on 27th July. It was the only Bf.108 to serve with the Austrian Air Force and when Germany annexed Austria, it went back to serve with the Luftwaffe.
• Bulgaria: During the war Bulgaria bought a total of six Bf.108 in 1941. They were assigned to the 1st Courier Squadron but were used mainly for training purposes.
• Independent State of Croatia: The 15.(Kroat)/JG.52 squadron composed by Croatian pilots who fought in the Eastern Front, used some Bf.108 for liaison purposes outside combat zones. The one depicted below was used by four Croatian pilots on 19th September 1942 to fly to Uman, in the USSR, where they were based.
• Hungary: In 1937 the Royal Hungarian Air Force bought a total of seven Bf.108 which were used in a wide range of duties. From liaison, communications and even trainer. They served through the war on the Eastern Front and until the end of the war.
• Romania: The Royal Romanian Air Force had at least one Bf.108 at the beginning of the war. It was assigned to the 11th Courier Squadron which belonged to the 1st Air Corps. During 1943 and 1944 it was still in service.

Sources:

1. https://en.wikipedia.org/wiki/Messerschmitt_Bf_108

2. http://www.warbirdalley.com/bf108.htm

3. Wydawnictwo Militaria 149 - Messerschmitt Bf-108 Taifun

Messerschmitt Bf.109G - Bulgarian users

From 1941 onwards, the Royal Bulgarian Air Force received many new German equipment, among them the famous Bf.109E, as they got 15 of them. Later in the war, as the American bombers which were on their way to bomb Ploesti, in Romania, had to cross Bulgarian soil, the Bf.109E proved to be outdated, so the decission of adquiring many of the new Bf.109G was taken.
A total of 145 Bf.109Gs were adquired and assigned to the various squadrons of the Royal Bulgarian Air Force.
They took part in the aerial defence of the country as the Allied raids intensified and was the fighter of choice for the top Bulgarian aces in history. Among them Stoyan Stoyanov which is depicted below and he flow that aircraft until being promoted to the command of 3.6 Orlyak (3.6 squadron) and after that it passed to his successor pouruchik Petar Manolev.
It was also the aircraft of podporuchik of S Marinopolski who painted the name of his girlfriend Helga under the cockpit and applied it to make it look like kill marks from a distance. Poruchik Ditmar Spisarevski managed to shot down an American B-24 Liberator on 20th December 1943 manning his Bf.109G-2 and, according to eyewitness he managed to shot down a second one by a ramming attack, although only the first one was officially recognized. The application of his individual number in yellow indicates that the aircraft belongs to the staff of the 3.6 orlyak.
The last batch of Bf.109Gs that Germany supplied to Bulgaria in mid-1944, included some late production Bf.109G-6s with the famous Galland hood.
Once Bulgaria switched sides in September 1944, the Bf.109Gs kept serving with the Bulgarian Air Force with the new pro-allied markings which they served with until the end of the war.
It seems that shortly after the war, in mid-to-late 1945 they were gradually replaced with the Soviet-made Yakovlev Yak-9.

Sources:
1. https://en.wikipedia.org/wiki/Messerschmitt_Bf_109_operational_history
2. http://www.lasegundaguerra.com/viewtopic.php?t=4091 (translated)
3. Osprey - Aircraft of the Aces 58 - Slovakian and Bulgarian Aces of World War 2 

Messerschmitt Bf.109E - Bulgarian users

The Royal Bulgarian Air Force bought a batch of 580 Messerschmitt Bf.109E-3 and E-4 during 1940 and 1941. Those aircraft equipped their fighter squadrons.
As Bulgaria was part of the Axis powers, they were forced to declare war on Yugoslavia when Germany attacked in April 1941 so Yugoslavia started to make reconnaissance flights over Bulgaria and even some Yugoslavian Dornier Do.17 bombed Kyustendil, a small town close to Yugoslavian border, followed by small bombardments against some other targets as airfields where some Luftwaffe units were stationed, Sofia's railway station and some other smaller villages. Later it was revealed that those air raid were conducted by RAF units stationed in Greece, however, as most of the opposition to those raids was made from anti-air ground fire, the inefficiency of the Bulgarian Air Force was obvious as the Bulgarian pilots lacked training.
The truth air war came to Bulgarian during 1942 and 1943 when the Allied targeted the oil fields of Ploesti, in Romania, and they had to pass through Bulgaria in order to arrive there. The Bf.109E performed wheel enough for being outdated shoting down some American bombers.
When Bulgarian switched sides in 1944 they continued serving with the Bulgarian Air Force until the end of the war and even in the inmediate postwar as it's known that most of them were sold to Yugoslavia in 1949.

Sources:
1. https://en.wikipedia.org/wiki/Messerschmitt_Bf_109_operational_history
2. Osprey - Aircraft of the Aces 58 - Slovakian and Bulgarian Aces of World War 2
3. Salamander Books - The Complete Book of Fighters

Arado Ar.196 - Foreign Users, part two

In this second post about the mighty Arado Ar.196, we are covering its usage with the Bulgarian Air Force.
Bulgaria bought from 9 to 12 Arado Ar.196 A-3 (the exact number changes depending on the source you check) in 1943.
They were assigned to the 161. Jato commanded by Captain Kolarov and they operated from the bases of Varna and Burgas, both of them in Bulgaria.
When the war was over, they kept serving with the Bulgarian Air Force until 1947 when they were written off.
One of them made it to this day and nowadays is being exhibited in the Bulgarian Museum of Aviation located in Plovdiv.

Sources:
1. http://www.kagero.pl/index.php?option=com_content&view=article&id=303:arado-ar-196&catid=95&Itemid=688&limitstart=4
2. https://en.wikipedia.org/wiki/Arado_Ar_196

Avia B-135, Bulgarian Users

The Avia B-135 was a Czechoslovak monoplane fighter that was used by Bulgaria.

Back in the late 1930s, the Bulgarian DAR company bought a license to locally build the Avia B-135, which was to be known as the DAR 11 Lyastovitsa (Bulgarian word for "Swallow") but the DAR factories proved to be unsuitable for producing the airplane and only the 12 Czechoslovak made fighters ended serving in the Bulgarian Air Force.

As they were giving engine problems, they were mainly used on training duties. However, four of them were used in combat on 30th March 1944 when they intercepted some USAAC bombers returning from a bombing mission in Ploesti, Romania. Apparently an Avia B-135 piloted by Yordan Ferdinandov managed to shot down a B-24 bomber which crashed into Bulgarian soil that day.

Sources:
1. https://en.wikipedia.org/wiki/Avia_B-135
2. Salamander Books - The Complete Book of Fighters

Avia B-534-IV Bulgarian users

In the summer of 1939 the Bulgarian Air Force bought 78 B-534 from Germany. These were initially assigned to the 2. Istrebitelen Orlyak (2nd Fighter Air Regiment) and to the training squadron.

The last batch of this airplanes to arrive to Bulgaria was in March 1942 when 6. Istrebitelen Orlyak received some B-534-IV.
On 1st August 1943 they took part on the biggest operation this airplane would take part on when seven of them made two passes at American Consolidated B-24 Liberator bombers which were coming back from bombing Ploesti, in Romania. Even if they hit some B-24, not a single one of them were shot down due to the small calibre of their machine guns.
Some of the B-534-IV were damaged and crecked up on landing.
After Bulgaria switched sides on 9th September 1944, the B-534-IV were oftenly used in the ground attack role against German units and it's known that some B-534-IV were involved in a brief melee with six German Bf-109 at low altittude. One B-534-IV was lost and the Germans quickly broke off from combat aware of the high maneouvrability of the B-534-IV at low altittudes.

Sources:
1. https://en.wikipedia.org/wiki/Avia_B-534
2. http://surfcity.kund.dalnet.se/avia_bulgaria.htm
3. Salamander Books - The Complete Book of Fighters

Avia B-534-III

Following the sales success from the II series, the Czechoslovak Air Force ordered another batch of B-534 to be made.

In 1936 a second order was placed to Avia to manufacture more B-534. The first 25 of them belonged to the B-534-III denomination and were started in the second half of 1936. The III series featured some minor changes like aerodynamic refinements which saw the frontal carburator's air intake streamlined. Mudguard spats were also added, however as they tended to clog, they were usually removed.

This was the least produced variant before switching to the famous B-534-IV version, which was a success in sales. However, it was used by many countries like Bulgaria, which used it in very limited numbers, Germany or Slovakia.

Sources:
1. https://en.wikipedia.org/wiki/Avia_B-534
2. Salamander Books - The Complete Book of Fighters