The Polikarpov I-15 was a biplane fighter that was developed in the interwar period and would go on to see extensive use during the Spanish Civil War, the Second Sino-Japanese War, the Battle of Khalkin-Gol, the Winter War, and World War II. While the I-15 was a quality aircraft for its time, it quickly became obsolete in the face of rapid advancement in aviation design the world over. Nevertheless, it continued to be used for a number of years in several different roles, and was an integral part of the Soviet Union’s first line of defense against the Luftwaffe in June of 1941. Severely outclassed by Germany’s Messerschmitt Bf-109 fighter, the I-15 played the vital role of holding the line against the German military’s onslaught during the early stages of the war when failure to do so would have been disastrous. Despite suffering heavy losses against the Luftwaffe, the I-15s did manage to help fight off the advancing Germany military for long enough for the Soviet Union to receive Lend-Lease fighters from the West and for the Soviet aviation industry to begin mass producing advanced fighters such as the La-5/7 and Yak-7/9/3.

The development of what would come to be the I-15 started in 1924, when Nikolai Polikarpov began work on his first biplane fighter: the 2I-N1. While serial production of this early fighter was not pursued, it did serve as a basis for Polikarpov’s future designs, including the I-3 and I-5. Produced between 1931 and 1934, production totals for the latter would reach more than 800. In 1933, Polikarpov sought to a develop a new fighter with increased speed and maneuverability, which resulted in the I-14a gull-winged radial-engine biplane. As Pavel Sukhoi was developing a monoplane fighter with the designation I-14 at the same time, the decision was made to redesignate Polikarpov’s new aircraft I-15, with the prototype number TsKB-3.

Construction of the first TsKB-3 was completed in October of 1933, with state trials undertaken later in the year. During factory and state testing, the new biplane did not fail to impress Soviet test pilots and engineers. With an ability to reach 5,000 meters (16,250’) in just 6.2 minutes, and the fact that it could make a 360-degree turn in only 8 seconds (which set a record), the TsKB-3 proved to be more maneuverable than any other Soviet fighter at the time.  Indeed, famed Soviet pilot Valeriy Chkalov himself carried out the flight tests, and was enthusiastic about the new biplane fighter’s maneuverability.

TsKB-3 prototype. Photo source: Airwar.ru

Even before the TsKB-3 underwent state acceptance trials, preparations were underway to mass produce the biplane fighter. Looking to speed up the Soviet Union’s technical advancement in the field of aviation, Soviet leaders in the early 1930s sought cooperation with aircraft companies in the US and Western Europe, both to import aircraft and to obtain licenses to produce aircraft engines and components (and entire airplanes) domestically. In April of 1933, an agreement was reached with Wright Aeronautical that gave the Soviet Union a license to build Wright’s new R-1820 9 cylinder radial engine, complete with blueprints and technical assistance. These engines would be used for serial-production I-15s (among other aircraft). The first Soviet-built Cyclone, given the designation M-25, was built in the summer of 1934, and serial production the license-built engines began the following year in the city of Perm. At first, the engines were produced from kits that were provided by Wright, with the only major difference between the R-1820 and its Soviet-built version being the latter’s use of metric components. By the end of 1935, however, the workers at Factory No. 19, led by Chief Designer and Technical Director Arkadiy Shvetsov, had obtained the technical know-how and domestically-built components to produce the engine without assistance from Wright. By the end of the year, a total of 660 M-25s had been built.

However, serial production of the I-15 was given the greenlight in early 1934, before production of the M-25 had been launched. Consequently, initial production aircraft were powered by imported Wright Cyclone engines. Others were powered by the M-22, a license-built version of the Bristol Jupiter radial engine. Despite the fact that the M-22’s output was 150 horsepower less than the M-25, the I-15s powered by the former could reach a top speed of 347 km/h, roughly 20 km/h less than the Cyclone-powered TsKB-3/I-15s. It wasn’t until early 1936 that Factory No. 19’s M-25s were mated with the I-15 airframe.

The baseline I-15’s armament consisted of four PV-1 7.62 mm machine guns, and it had the ability to carry four 10 kg (22 lb) bombs under the wings. The airframe itself was a mixed construction, and its defining physical feature was the gull-shaped formation of its upper wings. The TsKB-3 prototypes were equipped with Hamilton Standard propellers, but serial production I-15s utilized Soviet-built two-blade fixed-pitch propellers.

The first I-15s began entering service with VVS units as early as the end of 1934. While Soviet pilots enjoyed flying the new fighter, the biplane proved to be unreliable, as it suffered from frequent mechanical issues. For example, problems were often caused by the M-25 engines, which were installed without dampers, and consequently made the aircraft vibrate, which in turn added additional stress on the airframe. Moreover, fuel and oil leaks were a constant problem, and the wheel spats would at times become clogged with grass which would cause the aircraft to flip on its nose during landings. These and other glaring issues led the Soviet leadership to pause production of the biplane while Polikarpov worked to eradicate the aircraft’s deficiencies. Meanwhile, Polikarpov’s I-16 monoplane was being delivered to frontline units for the first time. Ultimately, VVS commanders preferred the I-16 over the plagued I-15, and the decision was eventually reached to cease production of the former after only 384 had been manufactured.

Nevertheless, a number of I-15s remained in service with the VVS and, more significantly, they were sent to the Spanish Republican Popular Front Government and were used against Franco’s Nationalists during the Spanish Civil War. In October of 1936, the first shipment of M-22-powered I-15s arrived in Cartagena. The shipment contained enough fighters to form two squadrons, which were initially manned mainly by Soviet “volunteers”. When more Spanish pilots entered the ranks of the two squadrons, the I-15 was affectionately nicknamed Chato (snub-nosed). The I-15s first saw combat on November 4, 1936, and were credited with shooting down two Ju-52/3ms and two CR-32 fighters. No Chatos were lost. During a separate battle on the same day, I-15s claimed four He-51s shot down. Over the next several days, another 12 enemy aircraft were claimed by the I-15 squadrons for the loss of two Soviet fighters. By the end of November, the I-15s had claimed 60 enemy aircraft shot down, a rather ambitious exaggeration. Nonetheless, during this period the Chatos were successful in defending Madrid from the Nationalists, causing the latter to temporarily halt daytime bombing sorties. However, with the introduction of more advanced German fighters, the I-15’s success eventually faded.

Spanish I-15. Photo source: Airwar.ru

Deliveries of I-15s to the Republicans continued until the summer of 1937, when another two batches of M-25-powered Chatos arrived. While the exact number of I-15s delivered to Spain is unknown, historians estimate the number to be between 139 and 155. Meanwhile, the Spanish Republicans themselves were manufacturing I-15s under license, an agreement that was reached in early 1937. In all, the Republicans would build 237 I-15s. However, the number of airworthy Chatos continued to decrease throughout the course of 1937 and 1938, in part due to normal wear and tear on the aircraft, and in part due to the fact that the Nationalist side began introducing German Messerschmitt Bf-109s and Italian Fiat G.50s, aircraft that outclassed the now obsolete Chato. However, as would be demonstrated on a much larger scale during the Second World War, skilled Polikarpov pilots could achieve a certain (small) degree of success against the German Messerschmitts, given the right circumstances.  A Republican I-15 pilot, Joaquin Calvo Diago, told Carl A. Posey years later, “The Chato is simpático… was very maneuverable against the 109 [the Messerschmitt Bf 109]. It climbed well.” Nevertheless, the German pilots did show that more often than not, the I-15 was no match for the Bf-109, and Chato losses continued to increase exponentially. Indeed, by the end of the war, of the 1,400 Soviet aircraft of all types that had been sent to Spain during the Civil War, 1,176 had been destroyed (83%). Ultimately, the Republicans and their Soviet allies lost the war, though a total of nine Soviet I-15 pilots were awarded the Gold Star Hero of the Soviet Union during the fight against Franco’s Nationalists. At war’s end, the victorious Nationalists had captured 53 flyable Chatos, and they remained in service with Franco’s forces until 1950.

Meanwhile, an improved variant of the Chato, the I-15bis, was reaching VVS units back in the Soviet Union. When serial production of the I-15 was halted in 1935, Nikolai Polikarpov was urged by the Soviet leadership to work on a modification of the biplane that would eradicate many of the deficiencies of the I-15 and would also improve the fighter’s performance. The resulting prototype, TsKB-3bis, featured a longer span un-gulled upper wing that was modified in response to Soviet pilots’ complaints that the gulled wing of the I-15 restricted visibility. It was also equipped with an upgraded M-25V engine, and a larger engine housing which incorporated the entire frontal section of the fuselage. These modifications brought the serial I-15bis’ top speed to 379 km/h (256 mph), 29 km/h more than the baseline I-15. Like its predecessor, the I-15bis was armed with four 7.62mm PV-1 machine guns. However, the I-15bis could carry an additional 50kg (110 lb) of ordinance, bringing its total payload to 150 kg (330 lb). Moreover, it could carry up to six RS-82 rockets, which were found to be useful against German targets during WWII. The TsKB-3bis completed state trials in the fall of 1937, and entered serial production shortly thereafter.

I-15bis in flight. Photo source

A number of I-15bis’ were sent to Spain during the final stages of the Civil War, but arrived too late to see action. Nevertheless, the bis did see extensive combat even before Germany’s launch of Operation Barbarossa in June 1941. In November 1937, a batch of I-15s and I-15bis’ complete with Soviet “volunteers” was sent to the Nanking area to support the Chinese military against the invading Japanese forces. Flying primarily against Kawasaki Ki-10 biplanes, the I-15bis performed well against their obsolete Japanese counterparts, with the Ki-10s suffering heavy losses. Consequently, the Japanese leaders replaced the obsolete outdated biplanes with the modern Mitsubishi A5M2a monoplane fighters, which proved to be faster than the I-15bis, though less maneuverable. During air combat between the two types, it was found that the outcome was determined primarily by the skills of the pilots and the effective use of tactics as opposed to technological superiority, and the I-15bis’ combat performance against the A5M2a was therefore mixed. In January 1938, the VVS leadership decided to replace the I-15bis squadrons with I-16 squadrons, as it hoped to assess the capabilities of the latter against the A5M2a. However, I-15bis fighters were also given to the Chinese Air Force, which continued to fly the biplane fighters for some time, receiving a total of 186 examples from the Soviet Union. Despite some success shown by Soviet pilots over the A5M2s, Chinese airmen were typically poorly trained, and combat losses were consequently high. However, there were a number of highly-skilled Chinese pilots who flew the Soviet biplane, including ace Liu Chung-Wu, who scored 4 of his 7 victories while flying an I-15bis. The outcome of each individual aerial battle in the skies over China (and in every other theater, for that matter) relied on a multitude of factors, such as numerical superiority and quality of pilot, and was not determined solely by the type of aircraft involved. For example, in April of 1938, a force of 12 Ki-10s and three new Ki-27s claimed 24 I-15bis’ shot down in a single air battle. However, later that month, a mixed force of Chinese I-15bis’ and Soviet I-16s claimed 36 Japanese aircraft shot down. The Soviet-built biplanes were eventually superseded by deliveries of US-built aircraft to the Chinese forces.

The I-15bis was also used extensively by Soviet forces during the Battle of Khalkin-Gol against the Japanese military in the summer of 1939. While the bis performed well against the Mitsubishi A5M2a, the appearance of the faster Nakajima Ki-27 caused problems for VVS airmen. Indeed, Soviet pilots, in general, enjoyed success during the Battle of Khalkin-Gol, but by this time, the I-15bis proved to be obsolete compared to the Japanese Ki-27 and the VVS’ other two fighters (I-16 and I-153). By August, the poor performance of the I-15bis prompted the VVS leadership to relegate the biplane to reconnaissance and night patrol duties. However, despite the fact that the I-15bis was the Soviet air arm’s worst fighter, the presence of the more obsolete I-15bis’ was used to the VVS’ advantage. Due to the fact that the bis did not have retractable landing gears, Soviet pilots who flew improved Polikarpov I-153 biplane fighters would bait Ki-27s into attacking by flying with their landing gear down, making the Japanese pilots think they were inferior I-15bis fighters. Once the Ki-27s would get within range of the I-153s, the latter would raise their landing gears, apply full throttle, and engage the oncoming Japanese aircraft. Though the Red Army and VVS was victorious at Khalkin-Gol, the successful performance in the air was due primarily to I-16 and I-153 fighters. Nevertheless, the I-15bis’ career was far from over.

Despite the Red Army’s convincing victory against the Japanese, the Soviet Union’s next combat operation, the Winter War with Finland, which began on November 30, 1939, was not nearly as successful. Though significantly outmanned and outgunned, the Finnish military was repeatedly able to repel the Red Army until the Soviets eventually broke through in March of 1940. The VVS, which deployed 2,500 aircraft (mostly Tupolev SB bombers) at the outset of the war, enjoyed air superiority for most of the conflict. Nevertheless, the Finnish Air Force, which had only 114 combat aircraft fit for duty at the end of 1939, inflicted severe damage against the VVS, shooting down 200 Soviet aircraft during the war and losing only 62 of their own. However, the losses suffered by the VVS were indicative of a larger problem within the Soviet military in general (decimation of military leadership during the purges), and were not necessarily reflective of the aircraft flown by Soviet pilots. Indeed, the primary Finnish fighter, the Fokker D.XXI, was roughly equivalent to the Japanese Ki-27. The I-15bis comprised approximately 30% of the Soviet fighters committed to the war against Finland, though more often than not they were relegated to non-fighter duties.

Though the air battles fought against Japan and Finland had demonstrated the obsolescence of the I-15 and I-15bis fighters, when Germany invaded the Soviet Union in June of 1941, the VVS still had roughly 1,000 I-15s and I-15bis’ in their arsenal. Soviet pilots and ground troops recall how, on the first days of the war, the Polikarpov biplanes went up against the much faster Luftwaffe fighters and bombers, often with disastrous results. Leonid Mikhailovich Felman, a signals officer stationed in Kremenchuk in what is today central Ukraine, recalled the performance of the I-15/I-15bis on the first day of the war. “Biplanes- I-15bis. They said they showed themselves well in the battles with the Japanese [Khalkin Gol]. But this plane could catch up with neither Messerschmitts nor Dornier-13s. I asked the pilots: ‘well, how can you shoot down a plane, even if you can’t catch up with it?’ They said, ‘we must try to climb to get a speed equal to this plane’. But this, unfortunately, did not work.” An Il-2 Sturmovik pilot, Valentin Ivanovich Belikin, likewise remembered,  “….the SB was called a ‘high-speed bomber’ [SB= skorostnoi bombardirovshchik, fast bomber]. And its speed was very low, like our fighters! When we were in Armavi, they bombed us and bombed the city. Our fighters could not catch up with them: neither the Heinkel-111s nor other bombers. Our fighters were I-16s and I-15bis’! Because they had a lower speed! Why fight?! Us?! Against the Germans?! Well, no.”

Despite the abysmal performance of the I-15/I-15bis on the first days of the war, a number of Soviet pilots did achieve some success against their adversaries. Though the Polikarpov biplanes were slower than their German counterparts, their maneuverability was remarkable against the Bf-109s, and skilled Soviet pilots learned to accentuate the flight characteristics of the I-15s/I-15bis’ against the Luftwaffe’s superior aircraft, which enabled the occasional aerial victory over the Messerschmitts. Other pilots relied on luck in the face of German fighters. I-15bis pilot Vasiliy Kubarev recalled, “It was on this type of plane that I was able to shoot down my first plane- it was an Me-109 [Bf-109]. Four rockets were suspended under the plane. Well, when a lot of enemy planes appeared ahead of me, I released all four… all at once, without any interruption… he went into a flat corkscrew and fell to the ground…. The rest of the Germans turned and immediately left.” However, it must be stressed that, more often than not, the I-15 was no match for the Bf-109. “Our ‘Ishaks’, I-15s and I-16s were maneuverable,” one Soviet tank driver recalled, “but the Messers beat them mercilessly.”

I-15bis. Photo source: Airwar.ru

While the I-15/I-15bis floundered as fighters in the face of highly-trained Bf-109 pilots, the biplanes were slowly replaced by MiG-3, LaGG-3, and Yak-1 monoplanes, which relegated the Polikarpovs to ground attack roles, a capacity in which they had a greater degree of success. The biplanes lacked armor and were consequently susceptible to even small arms ground fire, but as anti-aircraft gunner Dmitry Poltavets noted, I-15bis and I-153 pilots who were tasked with carrying out grand attack missions against Axis positions developed tactics to protect the fragile biplanes from ground fire. “The fighters stationed at the airfield that we were instructed to guard, helped the infantry repel enemy attacks- they attacked Romanian trenches every day, threw hand grenades and small bombs. And they did everything intelligently. For example, one fighter would dive, and the second would immediately enter a dive to fire bursts at the enemy and protect the one who was coming out of the dive so that he was not shot down by rifles and machine guns, because the I-15bis and I-153 were poorly protected even from rifle fire. Apparently, for the enemy, such ground attacks were extremely unpleasant, because soon German planes began to bomb our airfield.”

The Polikarpov I-15 and I-15bis continued to serve in frontline units until the end of 1942, by which time the Soviet aviation industry had begun recovering from its massive evacuation eastward and the VVS was receiving large numbers of Lend-Lease aircraft from the US and the UK. Nevertheless, the biplanes continued to be used for secondary tasks through the end of the war, including reconnaissance and training duties. Georgiy Afanasev, who would later go on to fly Yak fighters, remarked, “we learned on old stuff. I-1, I-15, I-15bis… Take off and land on the airfield, and turn… I initially flew the I-15bis- such junk, you understand.” A Sturmovik pilot, Valentin Averyanov, similarly recalled learning first to taxi using an I-15 without wings and then learning to fly solo in the biplane. “It is difficult to take off in it,” he noted. Another Soviet fighter pilot, Anatoliy Bordun, learned to fly at the Kachin Military Aviation School in the Crimea, where cadets flew I-15s and I-16s. One of his classmates was Vasily Stalin, son of Soviet leader Josef Stalin. As Bordun recalled, “for security reasons, Vasily Stalin was trained separately. We had one instructor for a group of eleven people, and he had his own individual- Captain K.V. Marenkov, the best instructor at the school. In addition, Vasily Stalin had a separate hangar, where the aircraft that he flew- a DIT-2 and an I-15- were kept. The school management apparently decided that the I-15 was still safer than the I-16. Vasily’s planes were painted red. And we were instructed that when a red plane was airborne to not come close to it.”

At the time of its development, the Polikarpov I-15 was a modern fighter that was capable of taking on any potential adversary that was then in production. However, as is well know, aviation technology was advancing by leaps and bounds in the late 1930s, and what was one day a solid and advanced aircraft could the next day become obsolete. Though the Chato initially performed well during the Spanish Civil War, it was clearly outclassed by the Messerschmitt Bf-109s and Italian Fiat G.50s when the latter two entered service on the side of the Nationalists. Attempts to improve the I-15 in the I-15bis helped extend the model’s shelf life as a modern fighter for a short time, but it was once again outdone by the introduction of the Nakajima Ki-27 during the Battle of Khalkin-Gol. By the time Germany launched Operation Barbarossa in June of 1941, the obsolete I-15s and I-15bis’ were and integral part of the VVS’ first line of defense. While the biplane fighters were no match for the latest models of the Bf-109, they did serve a vital function during the early stages of the war: they staved off the German onslaught for long enough for Lend-Lease aircraft to arrive in large numbers, and for the Soviet aviation industry to mass-produce aircraft that were superior to the Luftwaffe’s fighters. By 1943, the Soviet Union was sending large numbers of advanced La-5 and Yak-9 fighters to the front, and the Western Allies were contributing thousands of Lend-Lease aircraft. Moreover, mass production of the Ilyushin Il-2 Sturmovik ground attack aircraft was in full swing. When it was no longer needed in these two roles, the I-15/I-15bis was used to train future Soviet pilots, which in and of itself is a vital function. The I-15/I-15bis may not have been a world-class fighter, but it certainly did the job required of it.

-Patrick Kinville

Bibliography:

• Istrebiteli Polikarpova. Voina v Vozdukhe. No. 136.
• Ivanov, Vladimir. Neizvestniy Polikarpov. Moscow: Yauza. 2009.
• Gordon, Yefim. Polikarpov’s Biplane Fighters. Red Star No. 6. Midland Publishing. 2002.
• Maslov, Mikhail. Polikarpov I-15, I-16, and I-153 Aces. Osprey Publishing. 2014.
• Posey, Carl A. “The War Between the Wars: In the skies over Spain, pilots and airplanes. Air & Space Magazine. April 30, 2009.
• Ya Pomnyu Project. www.iremember.ru