שילוב של מפציץ TB-3 ו i-16 שמחובר לכנף שלו

:Vakhmistrov started work on his idea of the long-range bomber escort in 1931. It was called “Zveno”, and its first incarnation involved two modified I-4 fighters strapped on top of the wing of TB-1 bomber. The first flight of this composite was successfully carried out on December 3rd 1931, over Monino base near Moscow.

Many more modifications, and flight-tests followed. The parasite planes were replaced with I-5’s, then a new, and bigger mother-ship arrived: TB-3. When Polikarpov I-16 monoplane fighters became available Valkhmistrov was eager to try them. Two I-16s were strapped under the wing of the big bomber, and this became the most successful configuration, known as Zveno 6. Carried on pyramidal suspension system, fighters were mounted under the wings of the TB-3 before flight. Connected to their behemoth “mother” with umbilical chords, they were feeding on fuel and oil during a joint flight. On take-offs, all six engines were throttled up, and roared in unison down the runway. It must have been such a sight.

Series of flights were carried out, with fighters successfully uncoupling from the bomber. Zveno 6 was finally accepted for production by NII-VVS (Scientific Research Institute of the Air Force) in December 1936.

Next was an attempt to enable the fighters to return to the mother-ship. Vakhmistrov had an idea of developing completely new, airborne fighter plane for Zveno, which wouldn't have landing gear, and as a consequence be smaller, lighter, and faster. This would also solve the problem of returning range of the fighters. A complicated tubular trapeze system was designed to extend and catch approaching I-16. Then, the whole thing would retract back, under the shadow of the gigantic wing. After several trials the process of reattachment was deemed too sensitive and complicated for an average skilled pilot.

The pinnacle of Zveno project came with “Aviamatka” flight, which took place in 1935. For the purpose of so called “airborne alert” no less than five different fighter planes were attached to one TB-3. Despite a successful flight, this concept was discarded by critics as just another publicity stunt by “Vakhmistrov’s flying circus”.

Final evolution of the composite that saw outbreak of the war, was based on Zveno-6, and was known as SPB Zveno. I-16s parasites changed their role from air defense to high speed dive-bombers. The success and effectiveness of SPB Zveno in its 30 combat missions was striking, especially considering that both TB-3, and I-16 fighters were already obsolete by the time they were called to defend the motherland. Bridges over Danube and Dniepr, oil fields, and docks of Constantsa, and other targets all fell victim to Zveno raids. German Field-Marshal, Erich von Manstein, in his memoirs implicitly blamed final loss of Stalingrad battle on Russian bombing of the bridge over Dniepr at Zaporozhje in August 1941. Two Zveno SPB composites were responsible for this attack. The bridge was not repaired before autumn of 1943, much to late for the fate of German troops. Despite their successes, the truth about Zveno missions remained secret to the outside world, long after the end of the war.