'Zveno-1' December 3, 1931
Involved Tupolev twin-engined TB-1 aviamatka (mother-ship) and two specially modified Tupolev I-4bis biplane fighters mounted above the wing of the bomber. The test took place over Monino with Zelevsky piloting TB-1, Chkalov and Anisimov at the controls I-4's and Sharapov and Vakhmistrov as observers. Both fighters were released simultaneously at altitude of 3,000 meters. Despite of the number of the mishaps the idea was found feasible and experiments were continued.
Zveno-1A September 1933
Consisted of A.N.Tupolev TB-1 mother-ship flown by Stefanovskij and two N.N.Polikarpov I-5 biplane fighters mounted on above the bomber wing. I-5s were piloted by Grozd and Kokkinaki.
Zveno-2 (or 2A) August 1934
Consisted of A.N.Tupolev TB-3 four-engined bomber piloted by Zalevskii and three I-5 fighters flown by Suzi, Suprun and Altnov. Two I-5s were attached on the top of the bomber's wings and third mounted above the fuselage. All three "took off" from bomber successfully.
Consisted of a A.N.Tupolev TB-3 bomber and two D.P.Grigorovich I-Z fighters suspended by a special attachment under the wings of the TB-3. Grozd and Korotkov piloted the I-Z fighters. Test flight ended tragically - Korotkov was killed in a collision with the wing of TB-3.
Zveno-5 April 1935
Single I-Z fighter was suspended under TB-3. The large steel-tube trapeze mounted under the fuselage of the bomber and hook-equipped fighter was able to engage and disengage in flight. Test pilot Stepanchenok was able to perform the maneuver. The randevu took place at 1,000m above Monino airfield. I-Z disengaged after few moments - TB-3 was not capable of landing with fighter underneath. TB-3 was flown by Stefanovskij and I-Z by Stepanchenok. Final hook-on was completed successfully on 23 March 1935 - first underfuselage hook-up in the world.
Zveno-6 August 1935
Involved a TB-3/AM-34 with two N.N.Polikarpov I-16 suspended between two large V-strut links under the wings of the bomber. Bomber was flown by Stefanovskij and fighters by Budakov and Nikishin.
Zveno-? November 1935
Culmination of the parasite fighter experiments was this Zveno consisted of two I-5 fighters fixed above and two N.N.Polikarpov I-16 mounted beneath the wings of TB-3/AM-34. The bomber was modified with under fuselage trapeze so that I-Z canon fighter piloted by Stepanchenok was hooked in flight. This combination consisted of six (!) aircraft of four various types. All fighters were released simultaneously. I-5s were flown by Nikishin and Suprun.
Zveno-SPB July 1937
Two N.N.Polikarpov I-16 type 5 dive-bombers were suspended under the wings of the TB-3/AM-34RN with Stefanovskij at the controls. Each I-16 flown by Nikolaev and Taborovskii carried two FAB-250 250kg bombs and were not able to take off under its own power with both full fuel load and 500kg payload. The takeoff weight of this Zveno was 22,000kg and top speed reaching 268km/h. Fighters were using the fuel of the mother-ship up to the moment of disengagement. Upon release I-16 within 50km of target fighters were supposed to return to the closest base. This zveno was adopted by Morskaya aviatsiaya of the VMF for anti-shipping operations. The combat unit was based at Yevpatoria equipped with six modified TB-3/AM-34RN and 12 SPB.
SPB was used operationally in WWII from Crimean bases against ships, bridges and other targets till 1942. Most famous combat mission took place on August 25, 1941 against Dunabe bridge at Chyernovod, Romania (railroad bridge to Constanta). The mission was successfully completed and bridge was destroyed.
Zveno-7 November 1939
Same as previous entry but three I-16 tip 5 fighter-bombers were used instead. Flown by Stefanovskij, Suprun and Nukhtikov.