November-Class submarine. Source: Wikipedia
K-8 was a November-Class Soviet submarine. The November class was the first class of Soviet nuclear attack submarines. This class of submarines suffered from reliability problems related to the ships' steam generators. The steam generators in these early nuclear ships frequently developed leaks.
Leakage from a steam generator tube allows very radioactive primary coolant to exit the reactor coolant loop and enter the non-radioactive steam cycle loop. This radioactivity, depending on the size and duration of the leak, can be hazardous to the crew. With the November Class' dual reactor design, it would seem feasible to shut a damaged reactor down, reduce the primary system pressure, and limp home.
K-8 developed steam generator leaks on three separate occasions. On one occasion however, the steam generator leak was so severe that one reactor experienced a Loss of Coolant Accident. The crew struggled to make repairs and to refill the primary coolant loop in order to prevent a core meltdown due to decay heat. Several of the crew received significant doses of radiation as well as radiation burns.
The end for K-8 came in a more mundane way however. In April of 1970, while operating at a depth of 400ft, a short circuit caused a fire, which spread to two compartments via the ventilation system. Both reactors were shutdown, and the captain ordered the ship abandoned. Things must have been hellish inside.
Fortunately, K-8 was part of a Soviet fleet exercise when the fire occurred, so help was nearby. A surface vessel was dispatched to tow her back to port for repairs.
Disabled submarines are difficult to keep afloat (even next to a pier), and the reason is this: Most of the ship is already submerged. This is partly due to the thickness of the pressure hull, but also the ship is designed to be pretty close to neutral bouyancy. When the main ballast tanks are full of air, a submarine will have positive bouyancy, but not a whole lot of it.
Submarines are not surface ships, so they are designed with round-bottom hulls. This makes them wallow badly on the surface in heavy seas. When a submarine pitches and rolls in the waves, air escapes from the main ballast tanks, which are vented at the bottom. With each wave, a little main ballast tank air spills out, and a little bouyancy is lost.
This air can be replaced by a couple of means. The first is a massive low-pressure roots blower that takes air in from a large snorkel mast, and forces water out of the main ballast tanks. This method only works if electrical power is available. With both reactors out of service, it is unlikely that the storage battery of K-8 could have supplied the LP blower with electrical power for very long.
The other method for replacing air in the main ballast tanks involves briefly "puffing" them with very high pressure air from the ship's air banks. I don't know the capacity of the high pressure air banks on this class of ship, but I do know the supply of air was not infinite. In any case, without having electricity to run a high-pressure air compressor, these would eventually run out of pressure be unable to displace water out of the ballast tanks.
The abandon-ship order of the captain of K-8 was countermanded when the towing vessel arrived. 52 crewmembers, including the captain, re-boarded the ship for the tow back to port. 73 crewmembers were taken aboard the towing vessel.
The ships encountered rough weather. After 80 hours of heroic but futile damage control, the K-8 flooded. Sadly, even though ships were nearby, she took 52 men with her, who are now on eternal patrol with her.