Soviet Zveno Aviamatka
In June 1931, Vladimir Sergeyevich Vakhmistrov of the NII VVS (Nauchno-Issledovatel'skiy Institut Voyenno-Vozdushnykh Sil – scientific test institute of the air force) started work on combinations of fighters rigidly attached to heavy bomber aircraft. The system was envisioned to serve several purposes:
- Delivery of fighters beyond their conventional range
- Provision of bombers with escort fighters
- Use of fighters for dive bombing with heavier bombs than they would be able to take off with on their own
- Using the added thrust of parasite aircraft to get a heavily laden bomber airborne.
In all Zveno configurations, all aircraft were piloted and all had their engines running — it was expected that the combined thrust would more than offset the weight and actually improve the performance of the mothership compared to conventional bombers. The fighters were rigidly attached via pyramid-shaped metal frames, with both latches controlled by the fighter pilots. (On Zveno-1, the front latches were controlled by the bomber crew, while the back latch was controlled by the pilot; this was changed to all-pilot control in the next version). The original design included umbilical fuel lines which permitted the fighters to use fuel from the bomber while attached, although this was not fully implemented in practice.