Zveno Project an Incredible Aviation Concept

The Zveno project, developed in the Soviet Union during the 1930s, was an innovative concept in the field of military aviation, envisioned by the aviation engineer Vladimir Vakhmistrov. This unique system combined a heavy bomber, either the Tupolev TB-1 or the Tupolev TB-3, with two to five fighter aircraft.

Depending on the specific Zveno variant, these fighter planes either launched together with the bomber or docked with it in mid-flight, and were capable of refueling from the mothership. The most definitive version of this system, known as Zveno-SPB, utilized a TB-3 bomber carrying two Polikarpov I-16 fighters.

Each of these fighters was armed with two 250 kg (550 lb) bombs. This strategic weapon system was employed effectively in combat, particularly against targets in Romania during the early phases of the German-Soviet War. The same squadron also executed a successful attack on a bridge over the River Dnieper, which had fallen under German control.


Development and Design

Conceived in the late 1920s under the direction of the esteemed aeronautical engineer Andrei Tupolev, the TB-3 was one of the world’s first all-metal monoplane heavy bombers, marking a significant leap in aircraft design.

Tupolev, already known for his innovative approach to aircraft construction, embarked on the design of the TB-3 with the intention of creating a bomber that could meet the demanding needs of the Soviet military.

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The result was an aircraft that not only boasted impressive size and payload capacity but also incorporated advanced design features for its era. The TB-3’s airframe was constructed entirely of metal, predominantly using corrugated sheet metal, which provided exceptional strength and durability – a critical factor for a bomber destined for rigorous operational use.

Zveno was a parasite aircraft developed in the Soviet Union during the 1930s.
Zveno-2: Tupolev TB-3 and three Polikarpov I-5. Also visible is the ramp for loading the fighters. The centerline aircraft was hoisted on top of the fuselage by hand.

The design of the TB-3 was distinguished by its sheer scale and robustness. The aircraft was equipped with four powerful engines, a testament to the emerging understanding of the need for significant power in heavy aircraft designs. These engines were mounted on the thick, straight wings of the bomber, providing the necessary lift and thrust to carry heavy payloads over long distances.

A key aspect of the TB-3’s design was its emphasis on practicality and functionality. Despite its size, the aircraft was surprisingly adaptable, capable of carrying a variety of payloads, including bombs and cargo.

Crew Comfort

This versatility was further enhanced by the TB-3’s ability to operate from rough airfields, owing to its robust undercarriage, which was designed to withstand the rigors of less-than-ideal runways that were common in the Soviet Union at the time.

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The TB-3 also showcased several innovative design elements for crew comfort and efficiency. The cockpit and other crew compartments were insulated and heated, a feature not commonly found in bombers of that era. This attention to crew conditions was indicative of Tupolev’s holistic approach to aircraft design, considering not just the technical and performance aspects, but also the human element of aviation.

In summary, the development and design of the Tupolev TB-3 were a remarkable achievement in the field of aviation. Under Andrei Tupolev’s guidance, the TB-3 emerged as a symbol of Soviet industrial and military capability, combining advanced engineering, robust construction, and practical functionality.

Its all-metal design, significant payload capacity, and adaptability set new standards in aircraft design and laid the groundwork for future advancements in heavy bomber technology.

Genesis of the Zveno Project

The genesis of the Zveno Project, a trailblazing concept, was rooted in the innovative vision of Vladimir Vakhmistrov, a Soviet engineer whose ideas were far ahead of his time. Conceived in the early 1930s, the Zveno Project was born out of a strategic necessity to enhance the operational range and effectiveness of fighter aircraft.

It consisted of a TB-1 or a TB-3 heavy bomber mothership and two to five fighters
It consisted of a TB-1 or a TB-3 heavy bomber mothership and two to five fighters

At its core, the project was an ambitious experiment in composite aviation, where smaller fighter planes, known as parasite aircraft, were carried aloft by a larger ‘mothership’ – in this case, the Tupolev TB-3 bomber.

Vakhmistrov’s idea stemmed from a keen understanding of the limitations faced by the fighter aircraft of that era, particularly their restricted range and payload capacity. The Zveno Project was envisioned as a solution to extend the operational reach of these fighters, allowing them to engage in missions far beyond their standard range.

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By attaching the fighters to a bomber, they could be transported over long distances, conserving fuel for combat operations near the target, thereby maximizing their effectiveness in battle. The concept was groundbreaking, as it proposed a radical departure from traditional aviation tactics and strategies.

Zveno Project a Technical Challenge

The TB-3, with its large size, robust design, and significant payload capacity, was identified as the ideal platform for this ambitious project. It had the necessary power and structural integrity to carry multiple fighter aircraft and deploy them in flight.

The Zveno Project was not just a technical challenge but also a strategic innovation. It aimed to revolutionize the way air warfare was conducted, by combining the long-range capability of bombers with the agility and combat prowess of fighters. This composite force could deliver a potent and surprise element in aerial warfare, enabling swift and unexpected strikes against targets that were previously out of reach.

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Moreover, the project was reflective of the bold and experimental spirit prevalent in Soviet aviation during this period. It demonstrated a willingness to explore uncharted territories in aerospace technology and tactics. The Zveno Project was a venture into the unknown, testing the limits of aviation capabilities and opening new possibilities for the future of military aircraft operations.

Zveno-1: The First Experiment

The core concept of this experiment was to test the feasibility of a ‘composite’ aircraft system, where the Tupolev TB-3 bomber would serve as a mothership, carrying fighter aircraft to extend their operational range dramatically.

Polikarpov I-5
Two synchronized 7.62-millimeter (0.300 in) PV-1 machine guns were fitted in the fuselage with 600 rounds apiece with an OP-1 telescopic sight.

This initial experiment involved the TB-3 bomber and two Polikarpov I-5 biplane fighters. The I-5s, known for their lightweight design and relative simplicity, were chosen due to their compatibility with the TB-3’s size and weight capacity.

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The TB-3 was modified to carry one I-5 under each wing, suspended on special harnesses that were designed to securely hold the fighters during takeoff, flight, and the initial stage of the descent. These harnesses also allowed for the quick release of the fighters when they reached the operation area.

The engineering challenges of Zveno-1 were substantial. The attachment of the I-5s significantly altered the aerodynamics of the TB-3, requiring careful consideration of weight distribution, drag, and lift.

Zveno was Groundbreaking

The release mechanism had to be meticulously designed to ensure the safe and swift detachment of the fighters without compromising the structural integrity of either the bomber or the fighters. Additionally, the pilots of both the TB-3 and the I-5s had to undergo specialized training to handle the unique flight dynamics of the composite aircraft.

The first successful trial of the Zveno-1 was a groundbreaking achievement. The TB-3, with its I-5 escorts, demonstrated that such a composite system was not only feasible but also had the potential to revolutionize certain aspects of aerial warfare.

The Tupolev TB-3, Heavy Bomber, civilian designation ANT-6
The Tupolev TB-3, Heavy Bomber, civilian designation ANT-6

The fighters, once released, were able to execute their missions with a full fuel load, giving them maximum combat time in the operation area. Following the completion of their objectives, the fighters could either rendezvous with the TB-3 for recovery or proceed to land independently, offering a flexible operational approach.

The success of Zveno-1 opened the door to further experiments in the Zveno series and demonstrated the potential for innovative solutions to the range limitations of fighter aircraft.

Operational Advantages

The Zveno-1 project, involving the Tupolev TB-3 bomber and Polikarpov I-5 fighters, presented a series of operational advantages and challenges that highlighted both the ingenuity and the complexity of this concept. One of the primary advantages was the significant extension of the operational range of the fighter aircraft.

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By being transported close to their targets by the TB-3, the fighters could save fuel for combat operations, allowing them to operate far beyond their usual range. This capability opened up new tactical possibilities, including the element of surprise in attacks, as enemy forces would not anticipate fighter assaults from such distances.

Another advantage was the enhanced strategic flexibility this system offered. The fighters, once released, could engage in various missions – from attacking ground targets to engaging enemy aircraft – before either rendezvousing with the TB-3 or landing independently.

This flexibility was particularly advantageous in the vast and varied terrain of the Soviet Union, where distances could otherwise limit the effectiveness of conventional fighter operations.

Attachment Points

However, the Zveno-1 project also faced significant challenges. The aerodynamic complexities of attaching fighters to a bomber were considerable. The TB-3 had to be carefully modified to accommodate the additional weight and drag of the fighters, which affected its flight characteristics.

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The attachment points had to be strong enough to hold the fighters during flight, yet allow for their quick release when needed. Additionally, the turbulence generated by the bomber and its effect on the fighters during takeoff and flight posed a significant challenge.

It was one of the world’s first cantilever wing four-engine heavy bomber.[2] Despite obsolescence and being officially withdrawn from service in 1939, the TB-3 performed bomber and transport duties throughout much of World War II. The TB-3 also saw combat as a Zveno project fighter mothership and as a light tank transport.

The process of launching and recovering the parasite aircraft was fraught with risk. The pilots of both the TB-3 and the Polikarpov I-5s required specialized training to handle the unique flight characteristics of the composite aircraft. Precise coordination and timing were crucial during the release and recovery phases to ensure the safety of both the bomber and the fighters.

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There were also logistical challenges in maintaining and deploying the Zveno-1 system. The modifications to the TB-3 and the I-5s required extensive engineering work, and the system demanded careful planning and coordination to execute missions successfully. Furthermore, the reliance on a large, vulnerable bomber to transport the fighters introduced an element of risk, as the loss of the TB-3 would also compromise the mission of the attached fighters.

Engineering Innovations

The Engineering Innovations and Modifications integral to the Zveno-1 project were a testament to the skill the Soviet aviation industry during the 1930s. To realize the ambitious vision of attaching fighter aircraft to a bomber, significant and innovative modifications were required, both to the Tupolev TB-3 bomber (the mothership) and the Polikarpov I-5 fighters (the parasite aircraft). And big sky thinking.

The TB-3 underwent extensive modifications to fulfill its role in the Zveno-1 project. Key among these was the development of a robust and reliable attachment mechanism. This mechanism had to securely hold the fighters during takeoff, flight, and the initial phase of descent, while also allowing for their quick and safe release when necessary.

TB-3 docking with a Grigorovich I-Z under the fuselage.
TB-3 docking with a Grigorovich I-Z under the fuselage.

The engineering challenge was to create a system that was strong enough to ensure the safety of both the bomber and the fighters during various phases of flight, including the increased turbulence during takeoff and landing.

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Furthermore, the aerodynamics of the TB-3 were significantly affected by the addition of the fighters. The aircraft had to be modified to handle the additional drag and altered weight distribution.

This included reinforcing the wing structure where the fighters were attached and adjusting the flight control systems to manage the change in flight characteristics.

Provided Valuable Insights

The Polikarpov I-5 fighters also required modifications. These included the addition of docking mechanisms that allowed them to be securely attached to and released from the TB-3. The airframes of the I-5s were strengthened to withstand the stresses of being carried aloft and released from a considerable height.

Additionally, modifications were made to their fuel systems and controls to ensure they could be rapidly activated upon release from the TB-3.

One of the most significant engineering feats of the Zveno-1 project was the synchronization of the release mechanism. The system had to ensure that the fighters could be detached simultaneously and safely, a task that required precise mechanical and aerodynamic design.

Polikarpov I-5
The I-5 was a single-seat biplane with the upper wing slightly larger than the lower

This was crucial to avoid collision between the fighters and the bomber upon release, as well as to ensure the immediate operational readiness of the fighters once detached.

The success of these modifications was evident in the successful flights and operations conducted under the Zveno-1 project. These engineering innovations not only solved the immediate challenges posed by the project but also contributed to the broader field of aviation technology.

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The lessons learned from the modifications and systems developed for Zveno-1 provided valuable insights into aircraft design, particularly in the realm of composite and multi-aircraft systems, influencing future aviation developments.

Operational Use

This extended range was particularly advantageous given the vast geographical expanse of the Soviet Union and the strategic necessity of projecting air power over distant territories. The ability to launch fighter attacks from unexpected locations and at greater distances from bases introduced a new element of surprise in aerial warfare, potentially catching enemy forces off guard.

After a successful trial period in 1938, the Zveno-SPB system was officially integrated into service. By February 1, 1940, the Soviet Air Force was slated to receive 20 TB-3 bombers and 40 I-16 fighters, with an identical allotment designated for the Soviet Navy.

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Concurrently, Vladimir Vakhmistrov was tasked to explore the feasibility of using other aircraft, including the Tupolev TB-7, Tupolev MTB-2, and GST (PBY Catalina), as motherships. There was also consideration of equipping the I-16 fighters with larger 500 kg (1,100 lb) bombs.

However, by 1939, governmental support for the Zveno project began to diminish. The Navy withdrew all its orders, and the Air Force reduced its fighter requirement from 40 to just 12. This change in stance was influenced by shifting military priorities and resource allocation.

Despite this, the early successes of the Luftwaffe’s Junkers Ju 87 dive bombers in the initial phase of World War II caught the attention of Soviet military strategists. Recognizing a gap in their own capabilities, as the Soviet Union lacked dedicated dive bombers, a decision was made to continue the Zveno-SPB project, albeit on a smaller scale.

Six Combinations

Testing for the first production model of Zveno began in June 1940. This variant was distinct from the prototype, employing the more powerful I-16 Type 24 fighters. Ultimately, six combinations of mothership and fighter aircraft were completed — six TB-3s and twelve modified I-16 Type 24s.

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These units were assigned to the 2nd Special Squadron of the 32nd IAP (Fighter Regiment) within the 62nd Aviation Brigade of the Black Sea Fleet Air Force, stationed in Yevpatoria, Crimea. This deployment marked a significant milestone in the operational use of the Zveno-SPB system, showcasing its strategic value in the evolving landscape of military aviation.

zveno bomber

During the German-Soviet War, the Zveno-SPB system was deployed in combat, albeit on a limited scale, and achieved notable success. In the early phases of the conflict, the Black Sea Fleet Air Force was assigned the mission of targeting industrial facilities in Romania, an ally of Nazi Germany.

A key target was the King Carol I Bridge over the Danube River, which was integral to the Ploieşti-Constanța oil pipeline, a crucial resource for the Axis powers.

Previous efforts to destroy this strategically important bridge using conventional bombers had been unsuccessful due to its heavy fortifications. This led to the decision to entrust the mission to the Zveno squadron, leveraging their unique operational capabilities.

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Prior to targeting the bridge, a combat test was planned to assess the effectiveness of the Zveno-SPB in a real-world scenario. The target chosen for this test was the oil depot at Constanţa.

On July 26, 1941, two Zveno-SPB aircraft embarked on this critical mission. The operation was conducted in broad daylight, a bold move considering the heightened risk of enemy detection and response. The fighters, each carrying heavy bombs, detached from the TB-3 motherships approximately 40 kilometers (22 nautical miles, 25 miles) from the target.


This strategic disconnection allowed the fighters to approach the depot, execute their bombing run, and then return independently to their home airfield. The mission was executed flawlessly, with the Zveno-SPB aircraft successfully striking the Constanţa oil depot and returning without any losses.

This operation not only demonstrated the tactical viability of the Zveno-SPB system but also highlighted its potential as a precision strike tool against high-value targets. The successful attack on the Constanţa depot set the stage for further operational use of the Zveno-SPB system in the German-Soviet War, marking a significant achievement in the history of military aviation and the innovative use of composite aircraft systems.

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The inaugural raid on the King Carol I Bridge by the Zveno-SPB units occurred on August 10, 1941. For this mission, the Polikarpov I-16 fighters were equipped with additional 95-liter (25 US gallon) underwing fuel tanks, providing an extra 35 minutes of flight time. Out of three Zveno-SPBs deployed, one had to return due to mechanical issues.

The remaining two launched their fighters about 15 kilometers (8 nautical miles, 9 miles) from the Romanian coast. The I-16s effectively performed dive-bombing from an altitude of 1,800 meters (5,900 feet) and managed to return to their base unscathed, despite intense anti-aircraft fire.

A second raid was executed on August 13, 1941. This time, all three Zveno-SPBs successfully reached the target area. The six fighters achieved five direct hits on the bridge, resulting in the complete destruction of one of its spans. On their return journey, the fighters also strafed Romanian infantry near Sulina and safely made it back to Eupatoria without any losses.

High-Output Mikulin AM-34FRN

Buoyed by these successful operations, two more Zveno-SPBs were brought to operational status, bringing the total to five. However, the availability of high-output Mikulin AM-34FRN engines, essential for lifting the heavy aircraft, was a limiting factor; other engine models lacked the necessary power for takeoff.

On August 16, 1941, Admiral Kuznetsov requested additional AM-34FRN-engined TB-3s from Joseph Stalin to convert them into Zveno-SPB carriers. However, this request was denied due to the Air Force’s heavy losses in the early stages of the war.

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Despite these setbacks, the five operational Zveno-SPBs continued to fly missions. They successfully destroyed a dry dock in Constanţa on August 17 and a bridge across the Dnieper River on August 28, although one I-16 was lost in the latter operation.

In a repeat attack the following day, four Zveno-launched I-16s engaged several Messerschmitt Bf 109s, successfully shooting down two.

Despite the high success rate of these missions, Zveno operations were discontinued by 1942. The primary reasons were the increasing vulnerability of the aging TB-3s and I-16s, which could not match the enemy’s growing air superiority.

It is estimated that the Zveno-SPB units carried out at least 30 combat missions, demonstrating their effectiveness in specific operational scenarios despite the challenges and limitations they faced.

Legacy and Historical Significance

The Zveno-1 project’s legacy is primarily anchored in its visionary approach to extending the operational capabilities of fighter aircraft. By effectively deploying parasite fighters from a larger bomber, the project demonstrated a remarkable solution to the range limitations faced by the military aviation of that era.

This concept of using a mothership to extend the operational reach of smaller aircraft was revolutionary, and it foreshadowed later developments in aerial warfare and aircraft design.

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From a historical perspective, the Zveno-1 project is a testament to the ingenuity and resourcefulness of Soviet aviation engineers during a period marked by rapid technological advancements and intense military competition.

The successful integration of different aircraft types into a single operational unit was a groundbreaking achievement that showcased the potential for innovative solutions in overcoming the constraints of contemporary aviation technology.

Furthermore, the project highlighted the strategic importance of flexibility and adaptability in military operations. The ability to launch surprise attacks from extended ranges and adapt to various mission profiles offered a new dimension to tactical planning and execution in aerial combat.

Parasite Aircraft

This aspect of the Zveno-1 project had lasting implications, influencing military strategies and the development of air-launched and composite aircraft systems in subsequent decades.

The engineering challenges overcome in this project laid the groundwork for future experiments in air-launched spacecraft and the development of modern airborne launch systems. The project’s success in synchronizing the release and operation of parasite aircraft from a mothership provided valuable insights that have been applied in various fields of aviation.

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In addition to its military implications, the legacy of the Zveno-1 project extends into the realm of aerospace innovation. The concept of composite aircraft systems, as pioneered by the Zveno-1 project, has found applications in space exploration and commercial aviation, where similar principles are used for satellite deployment and air-launch-to-orbit systems.

It stands as a symbol of early 20th-century innovation and foresight in military aviation, reflecting a period of remarkable creativity and advancement.

The project’s legacy continues to influence modern aviation and aerospace technology, underscoring its enduring significance in the evolution of aircraft design and operational strategy.


There are no known surviving examples of the Tupolev TB-3 bomber or the Polikarpov I-5 fighter that are intact or on public display. Both aircraft played significant roles in the early period of Soviet aviation but, like many aircraft of that era, have not been preserved for contemporary viewing.

The Tupolev TB-3, being a large and primarily metallic aircraft, was likely subject to recycling during and after World War II, a common fate for many older or obsolete aircraft due to the high demand for metal.

Similarly, the Polikarpov I-5, being an even earlier design and largely constructed of wood and fabric, would have faced deterioration over time, making preservation challenging.

However, it’s worth noting that the status of such historical artifacts can change, and new discoveries or restorations can sometimes bring these rare aircraft back into the public eye. Aviation museums in Russia or other countries with historical ties to the Soviet Union would be the most likely locations for any surviving parts or replicas of these aircraft.

Additionally, aviation enthusiasts and historians sometimes undertake projects to reconstruct or build replicas of historic aircraft, including those as significant as the TB-3 and I-5.