The SSBN Typhoon-class submarine, officially designated the Akula (“Shark”) in Russia, is a Cold War behemoth measuring 175 meters long and displacing 48,000 tonnes as it sinks.
That's double the tonnage of American Ohio-class SSBNs it was meant to compete with.
No less than five internal pressure hulls made of ultra-expensive titanium gave the Typhoon outstanding resistance to battle damage.
The Typhoon was the largest submarine ever built.