Do submarines ever sit on the bottom of the ocean?

WWII diesel boats did; but not nuclear boats, they would suck enough sand/silt/mud in thought seawater cooling pipes to fill up all of the exhaust steam condenser units and that would be bad. read more

Theoretically, if the feedwater intakes were on top of the sub, then it could potentially rest on the bottom, but the attitude would have to be constant adjusted with the ballast tanks, as the boat would have a tendency to roll over. read more

Ships from the Northern, Baltic, Black Sea, and Pacific fleets participated, roughly two hundred in all. The Soviet Northern Fleet deployed sixty surface ships and forty submarines in support of the operation. As per normal procedure, K-8 was carrying four torpedoes armed with nuclear warheads. read more