Belgorod-class

K-329 Belgorod is a Russian special-purpose nuclear submarine and, since the retirement of the last Typhoon, the largest operational submarine in the world at 184 meters. Laid down in 1992 as an Oscar II-class cruise missile submarine, its construction was halted by post-Soviet financial crises, briefly revived after the loss of its sister ship Kursk, and finally redesigned from 2012 as Project 09852 — a mothership for the Main Directorate of Deep-Sea Research (GUGI) and the launch platform for the Poseidon nuclear-powered, nuclear-armed underwater vehicle.

The rebuild replaced the cruise missile compartment with an 18-meter bay able to carry deep-diving special operations submarines such as Losharik, while the lengthened bow accommodates the Poseidon torpedoes — reportedly up to six on a revolving launcher. The Poseidon itself, about 24 meters long with a small nuclear reactor, is designed to cross oceans autonomously at around 70 knots to deliver a strategic warhead. Two OK-650M.02 pressurized water reactors drive the boat at up to 32 knots submerged, with an endurance of 120 days and a crew of about 110.

Belgorod was presented by Vladimir Putin alongside the Poseidon in his March 2018 address, launched in April 2019, and delivered to the Russian Navy on 8 July 2022. The submarine serves in a strategic and intelligence role rather than as a conventional combatant, and its movements — including reported deployments to Arctic waters — are closely tracked by NATO navies.