The TB-3 was also used in several special projects as a fighter mothership in the Zveno project and for delivering light T-27, T-37, and T-38 tanks. On 1 August 1941, a pair of TB-3s in "Zveno-SPB" configuration, each with two Polikarpov I-16 fighters carrying a pair of bombs, destroyed an oil depot with no losses in the port of Constanța, Romania. On 11 and 13 August 1941, "Zveno-SPB" successfully damaged the King Carol I Bridge over the Danube in Romania. Zveno operations ended in the autumn of 1942 due to the vulnerability of the motherships.