The Russian MoD plans to begin state tests of the unusual Project 09852 nuclear submarine Belgorod in May, once the ice melts in the White Sea.
This would mark a significant milestone in a programme that has experienced a series of setbacks and restarts since the submarine was laid down in 1992.
At 184m, Belgorod is the longest submarine in the world (12.5m longer than Dmitriy Donskoy, the last remaining Typhoon-class nuclear-powered ballistic missile submarine (SSBN) in the Russian Navy, and 13.3m longer than the Ohio-class submarines in USN service.
If state trials prove successful, Belgorod will be