Not only were the Soviets never idle in their research for composite aircraft, but they can even be considered pioneers in this domain as can be witnessed by the different tests they conducted in the thirties, especially those with their heavy four-engine Tupolev TB-3s. In the thirties, this airplane was the first strategic bomber in the history of aviation. It was also utilized for other diversified missions: sometimes equipped with gliding torpedoes, sometimes transporting paratroopers, sometimes performing polar expeditions, or transporting tanks…But, its most original utilization was that of an aircraft carrier, under the name "Samolyot Zveno".
Beginning in 1931, engineer V.S. Vakhmistrov understood the fallacies of G. Douhet's theories, more than ten years before the Americans invested, and felt over confident in the invulnerability of their heavy bomber groups because they were equipped with powerful defense armament. Understanding that those slow and not very maneuverable airplanes would make an easy prey for the fighters even when operating at high altitude, he considered placing among the bomber formations composite aircraft, namely some heavy bombers transporting fighters, thus developing the airplane "aircraft carrier" concept.
The first tests occurred on December 31st 1931 from a TB-1 twin engine airplane, transporting two modified I-4 fighters (the lower wing had been removed) perched atop the wing of the transporter. As a result of those tests, Vakhmistrov and the pilots were decorated and made recipients of the order of the red star. The range of the TB-1s being insufficient, the Zveno Z-2 which was comprised of a TB-3 transporting a Polikarpov I-5 on its fuselage and two on its wings was developed between 1933 and 1935. The object was the protection of the bomber formation, the fighter's engines were kept running during the entire mission permitting rapid intervention. The range of the fighters being obviously limited, they received their fuel supply from their transporter until their eventual separation.
In the 1934 configuration of the Zveno Z-3, two I-Z monoplanes were suspended under the wings of a TB-3 "Aviamatka" ("Mother-ship") by mean of folding trapezes. The first test was catastrophic, resulting in the death of the test pilot, and a breakdown in relationship between the Army and Engineer Vakhmistrov ensued. The development of Zveno 5 was the occasion of a world premiere ceremony. On April 5th 1935, at 1,000 meters over the Monino base, pilot Stepanchenok hooked up his monoplane I-Z to a trapeze deployed under the fuselage of a TB-3, achieving the first in flight "Rendez vous" in the history of aviation. Taking in consideration the configuration of Zveno 5, it was impossible for the TB-3 to land in the composite configuration, the I-Z had to release itself once again from the Mother-ship before the landing could be made.
It was the first step in answering the delicate question for the retrieval of the "parasite" fighter.
Certainly, the concept of bringing interceptors, or fighters to the combat arena seemed appealing, but those airplanes lacking the range to return to their lines after the combat mission provoked a question about their return trip which was not easily answered.
We can assume that it was this delicate question that caused the VVS (Air Forces) to reject this nonetheless seductive project of the Zveno Z-6, composed of a TB-3 and two I-16 type 5 suspended under the wings, but not retrievable in flight.
Vakhmistrow, (although a victim of the Stalinist purge) continued to work on his projects, and in 1939 he finally resolved the delicate question of the retrieval of the fighters with the Z-7, where the fighters could return and suspend themselves to the "Mother Ship". However, this project was not accepted, because if this maneuver was deemed delicate for test pilots, it would be much more difficult for a less experienced pilot. During military operations, this concept would have been as dangerous for the enemies as for the users! At any rate, operation "Barbarossa" and the rapid German advance put an end to this project.
Vakhmistrow's initial idea, which was the defense of the heavy bombers with interceptors carried aboard a "Mother Ship" was not the only idea that he formulated. As early as 1935, he found another application for his concept although not as spectacular.
Taking into consideration the important payload capacity of the TB-3, as well as the moral necessity to permit the range limited fighter to easily rejoin their lines, he thought of applying his composite system for the defense of sensitive areas, such as the urbane or industrial agglomerations.
Consequently, the only solution for maintaining an efficient surveillance aloft in the mid-thirties was to keep an important fleet of fighters airborne by mean of a continual relief system. The composite developed for this project was the "Aviamatka" PVO, consisting of an assembly of no less than six aircraft! This configuration was successfully tested in November of 1935, the TB-3 "Mother ship" took off with two I-15s on top of its wings, and two I-16s suspended under its wings. Once airborne, a trapeze was deployed and the I-Z flown by Stepanchenok proceeded with the hook up. Vakhmistrov even studied a configuration, which assembled more aircraft taking turn for suspended hook up under the wings of the TB-3. Although the VVS was not enthusiastic with the Zveno, the Navy showed some interest, namely for the Aviamatka PVO composite project considering its use for the protection of its ships and Naval bases.
Zveno for offensive mission
The Zveno composites had been conceived for defensive missions but they were never used operationally. They were however finally used for attack missions.
The stubborn Vakhmistrov in 1936 proposed a different configuration, not as spectacular as the previous ones, but one with a different purpose. The parasite aircraft would no longer be fighters, but Polikarpov I-16s equipped with two 250-kilo bombs. In the spring of 1941, the tests of the composite Zveno-SPB (Fast dive-bombers) proved conclusive. After many setbacks, orders and counter-orders, and while the aircraft were based in the Crimea, it was decided to use them against the ports and refineries installations in Romania. To guarantee the return of the I-16 bombers, they were equipped with an auxiliary fuel tank.
The first operational mission of the composites took place on the 26th of July 1936, during which time two Zveno-SPBs released their four I-16s near the Constanza harbor. Interesting detail: the FLAK did not even attempt to shoot them down, their presence so far from their bases being so hard to believe. The operation's success therefore brought a repeated utilization of the Zveno against the pipelines, bridges, and miscellaneous terrestrial objectives.
By the end of October 1941, the arrival of the German Wehrmacht at the Evpatoria factory where the Zveno were assembled put an end to those missions. None the less, it should be noted that despite the experimental nature of the concept, the results were interesting. In 29 sorties, only three I-16s were lost (no TB-3 were ever lost) and the percentage of the target destroyed was very significant.
The Zveno were an interesting concept due to their varieties of diverse utilization starting with a Tupolev TB-3 decidedly used for many roles. Within the frame of the German "Mistel" concept, that airplane was even tested as a flying bomb loaded with 3500 kilos of explosive, and Tele-guided by another airplane flying at its side.
© Aérostories, 2001.