When the Wehrmacht attacked Leningrad, they were met with some of the most powerful tanks in the world at the time: the Kirov prototypes. Among these were at least two KV-1s, already dreaded machines, armed with flamethrowers mounted in boxes beside the driver. Unlike other heavy flamethrower tanks, the KV-6 is not missing its hull machine gun. According to some sources, only one such tank was built, while others claim four were built. Photographs show at least two of these tanks were built, one of which was badly damaged by German forces, and the other captured.