K-535 Yuriy Dolgorukiy (Russian: ??? ???? ??????????) is a Borei-class nuclear-powered ballistic missile submarine of the Russian Navy, and the lead vessel of the class. Named after the founder of Moscow, Yuri Dolgorukiy, the vessel was laid down on 2 November 1996 and was first planned to enter service in 2001. However, project for the R-39M SLBM that the Borei class was supposed to carry was abandoned after several failed tests, and the submarine was redesigned for the new RSM-56 Bulava SLBM. The RSM-56 Bulava is smaller than the original R-39M, and in the 2007 START treaty data exchange it was reported that all Borei-class submarines would be equipped with 16 missiles instead of 12, as originally intended.