Zveno (Russian: Звено, a military unit "Flight") was a parasite aircraft developed in the Soviet Union during the 1930s. It was the brainchild of the aviation engineer Vladimir Vakhmistrov. It consisted of a Tupolev TB-1 or a Tupolev TB-3 heavy bomber mothership and two to five fighters. Depending on the variant, the fighters either launched with the mothership or docked in flight, and they could refuel from the bomber. The definitive Zveno-SPB using a TB-3 and two Polikarpov I-16s, each armed with two 250 kg (550 lb) bombs, was used operationally as a strategic weapon system with good results against targets in Romania during the opening stages of the German-Soviet War. The same squadron later carried out an attack against a bridge on the River Dnieper that had been captured by German forces.[