Zveno; The Soviet Flying Aircraft Carrier

June 22, 2023

The concept of the parasite aircraft carrier is one that has a long history; indeed I believe the first experiments were conducted in 1916.

The idea is that a large “mother” aircraft carries either one or more smaller ones, which can deploy from the host to perform their own missions. The concept is generally used as a means of boosting the range or operational sustainability of the smaller aircraft or else with the aim of offering protection to the “mother ship”. It has also been an idea that has been explored in theory and on occasion in reality a number of times throughout aviation history.

For example, in the 1930s the US Navy built the USS Akron and Macon – airships that effectively acted as flying aircraft carriers that could house and deploy up to five fighters. Another famous example is the McDonnell XF-85 fighter, which was intended to be carried by B-36 bombers and who would deploy the tiny jet to protect them from enemy interceptors as they approached their intended targets deep in the Soviet Union.

But these example, along with most other attempts to create parasitic aircraft combos, didn’t work particular well – or at least, not well enough to warrant full deployment. Indeed, the history of this rather niche idea is one full of experimentation, but very little practical value, and it pretty much fell by the wayside once aerial refueling was perfected.

Except…

It isn’t well remembered, but in fact a parasite aircraft combination did see combat. And apparently it proved successful enough that the operators advocated for a much greater adoption of the airborne aircraft carrier for operational use.

The Soviet Zveno program – colloquially known as Vakhmistrov’s Circus.

The origins of this date back to 1931 and started with the ideas of Vladimir Vakhmistrov, a pilot and glider designer serving with the Soviet Air Force. This organisation was undergoing a huge expansion and update at the time as a way of demonstrating Soviet progress and so Vakhmistrov’s rather advanced – and visually catching – ideas found fertile soil.

His proposal was that by having several fighters rigidly attached to a bomber aircraft that served as a mother ship, then a number of advantages were possible. At take-off, the combined output of all the respective powerplants could allow for heavier combined payloads to be carried. The smaller fighters would also now have much greater potential range, especially if they could draw fuel from the host bomber. This would allow them to act as escorts for their host, allowing for fighter cover to go right to the heart of a target area.

Certainly, the Soviet authorities liked the idea, and the first flight of the new concept aircraft combo flew in December 1931 – just six months after Vakhmistrov proposed it. This, the Zveno I, utilised a Tupolev TB-1 heavy bomber as mother ship while carrying two Tupolev I-4 fighters over its wings, with the fighters modified into monoplanes as their lower wing was not needed for take-off anymore and just added drag to the whole thing.

There was one hick up in this first flight when the crews messed up the order of release for the clamps holding one of the fighters, which led to it detaching prematurely, fortunately without serious consequences, but the second fighter was released correctly and broadly speaking the idea seemed to work.

Further development work led to an improved version of Zveno I, which changed out the I-4 fighters for a couple of Polikarpov I-5s that had better performance and were replacing the I-4s in service, with this configuration flying in 1933. There was also a further change made to create the -Ib, which fitted an I-5 over the aircraft’s fuselage, assumably for checking how this would affect flight characteristics.

The success of the experiments also led to other new aircraft being allocated for conversion and trials, and in August 1934 the Zveno II flew.

This took a Tupolev TB-3 heavy bomber, then one of the most advanced aircraft flying, and fitted it to carry three I-5s; two over the wings and a third over the fuselage. Though notionally an increase in deployable aircraft in fact the fuselage mounted I-5 seems to have been a bit of a pain to load and launch and ultimately had its wings and tail removed so as to act as an additional engine for the mother ship.

But with continuing support the next iteration of the Zveno, the -III was soon built. This changed things up by switching to carrying two fighters under the wings of the TB-3 instead of above them.

And selected for the parasite fighters was the Grigorovich I-Z. This rather odd and interesting aircraft was a monoplane which was armed with a single machine gun…and two single-shot 76mm recoilless guns. This set up however proved faulty and actually resulted in the entire types only fatal accident, which seems surprising considering the inherent dangers of launching aircraft from another, fast moving vehicle.

The new layout required the fighters to adjust their aircrafts locking posture after take-off, and during this one of the pilots misjudged the amount of stick needed and smashed his cockpit into the bombers wing. The incident killed the unfortunate pilot, but the Zveno III was able to make a successful emergency landing despite the damage.

I don’t know if there was a fourth model, but in March 1935 the Zveno V took to the air. This sought to examine the possibility of carrying an aircraft under the fuselage, which could only be achieved with the two aircraft taking off separately and then docking whilst flying. And it actually worked, with an I-Z managing to clamp onto the aircraft.

The follow up Zveno VI and VII sought to further test the ideas of underwing carriage, with the Zveno VI having two I-16 monoplane fighters attached before take off to a TB-3, while the -VII took this further by fitting trapeze arrangement that allowed the I-16s to attach while flying, allowing them to launch, then return to the mother aircraft when they had performed their mission.

This all led to one of the only practical, though I use the term loosely, airborne aircraft carriers to ever fly; The Zveno Aviamatka.

This saw the TB-3 fitted to carry not two fighters, not three, but five single-seat fighters. Composed of two I-16s under the wings, two I-5s mounted above them and a single I-Z on an under-fuselage trapeze, the Aviamatka was literally a flying aircraft carrier. And it worked, essentially, proving able to deploy and redock aircraft.

The idea was that the Aviamatka could conduct long-range, multi-aircraft patrols with one TB-3 supporting possibly up to eight I-16s, then the Soviet’s primary fighter. The aircraft could fly in shifts and when they needed to refuel dock with the mother craft and draw from that aircraft’s petrol tanks. This was anticipated to have allowed for a six-hour patrols to be conducted by the aircraft cluster.

Though it doesn’t seem that the full concept was ever tried out, docking and refueling of fighters was accomplished with Zveno VI and -VII, and so had interest remained in the idea then it was certainly feasible.

But by now it was 1937 and Vakhmistrov was thinking about other uses. The Soviet Air Force had lost much of its interest in heavy bombers, instead moving to a similar doctrine as the Germans with greater emphasis on tactical use for air power.

To be honest, the Soviets were pretty much correct at this point, as the technology and techniques to turn the heavy bomber into anything really more than a blunt instrument were still several years of hard combat experience away. At the time, if you wanted to accurately hit pinpoint targets, you needed dive bombers, a fact that was being demonstrated in the Spanish Civil War being fought at the time.

However, dive bombers tended to be smaller aircraft with limited range, intended more for tactical rather than strategic use. But with the Zveno, Vakhmistrov realized that now there existed the possibility of dive bombers being able to reach deep into enemy territory. And so, he developed the final model of the program, the Zveno-SPB.

This was a TB-3 that had two Polikarpov I-16 Type 5 fighters mounted under the wings, but now equipped not just with their machine gun armaments, but the ability to carry a pair of 250kg (550lb) bombs. This was a substantial increase in the I-16s bombload, which was only capable of lifting off with 100kg (220lb) of bombs on its own power, meaning that each Zveno mounted I-16 could carry five times the types standard load.

Another major advantage was that the aircraft also now had a substantial range increase, being carried to their target by the TB-3 before decoupling and attacking. While the I-16 was not a purpose-built dive bomber, this all meant that the SPB was a rather useful precision strike aircraft, especially for the day and age.

The other advantage was that the conversion basically used older aircraft and gave them a new lease of life, as the TB-3 was recognised as heading towards obsolescence already and the I-16 type 5’s also being replaced by better models.

And as the concept seemed to work pretty well, and utilised aircraft that weren’t particularly useful otherwise, there was a fair bit of enthusiasm for the -SPB and forty conversions were ordered. Vakhmistrov was even asked to examine the possibility of using current production aircraft like the new Pe-8 heavy bomber for use as Zveno aircraft.

But the period was one of huge disruption for the Soviet military due to Stalin’s paranoia, and his purge of the high command threw many plans into disarray, including procurement of the Zveno’s. Ultimately six service Zveno-SPBs were built based off Tupolev TB-3s for the mother ships and with twelve Polikarpov Type 24 I-16’s converted for usage as their parasite fighter bombers. These entered service in 1940 with the 2nd Special Squadron of the 32nd Fighter Regiment, based on the Crimean Peninsula, and the new aircraft were soon rejoicing under the nickname of “Shubikov’s Circus”, a nod to the unit’s commander.

As a result, the Zveno’s were available for combat service when the Soviet Union was invaded by Germany and their Romanian allies in June 1941. They were very soon able to prove their worth.

On July 26, just over a month after the beginning of the attack, two Zveno-SPBs took off carrying their four bomb-laden I-16 with the Romanian oil depot at the port city of Constanța their target. They approached to within twenty-five miles of the Romanian coast and deployed their attack aircraft. And these, as small fighter types, completely threw the air defences off.

After all, small single seat fighter bomber were well out of range from being able to launch an attack so far from Soviet air bases, and so the air defences seem to have assumed that the aircraft must have been friendly. They received a rude shock when the four I-16s swooped down and dropped their bombs into the oil facility and then, while the Ack-Ack crews scrambled for their guns, simply flew away, all returning under their own power to their base.

The attack, though a small affair, showed that the Zveno’s had a role to play and so other raids were planned, largely on tricky targets that heavy bombers couldn’t hit successfully. The primary target was the King Carol I rail bridge that crossed the Danube which in addition to being a critical logistic link also carried an oil pipeline that supplied the Axis war effort. Two raids by Zveno’s in August saw them inflict significant damage on this important target.

In total the Zveno’s conducted more than thirty missions between them, hitting a number of critical targets with a precision that conventional bombers couldn’t achieve. During these it is reported that only a single I-16 was lost to enemy action, but the little fighters claimed two Bf 109 fighters themselves as they could act in their original roles once they had conducted their bomb attacks. Indeed, so useful were the unusual combos proving that Admiral Kuznetsov himself is reputed to have asked Stalin for more conversions to be made.

But the situation was deteriorating fast, and the losses suffered by the Soviet Air Force meant that other missions and requirements took priority. It isn’t exactly recorded when the Zveno’s ceased operations, but certainly by 1942 they were no longer operating as carriers and, with the loss of Crimea to the Germans at around this time, assumably were destroyed in the fighting, with any further records destroyed in the chaos.

But they certainly represent an innovative, and intriguing, footnote in aviation history.

Sources/Related:

https://www.testpilot.ru/review/300x/02.php

https://en.m.wikipedia.org/wiki/Zveno_project

https://nationalinterest.org/blog/buzz/russia%E2%80%99s-bizarre-%E2%80%98sveno%E2%80%99-mothership-bombers-could-launch-fighters-their-wings-59282

https://en.wikipedia.org/wiki/Vladimir_Vakhmistrov

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