While the exact details of the Soyuz-M are not known, it is believed to be a two-stage rocket, derived from the Soyuz. It may have been similar to the later Soyuz-U. Following the cancellation of the Soyuz 7K-S, eight were launched with Zenit-4MT spacecraft. The first of these launches occurred on 27 December 1971, and the last on 31 March 1976. All launches occurred from the Plesetsk Cosmodrome, six from pad 41/1 and two from pad 43/4.