During the Cold War, the US could not build secret bases capable of housing capital assets like submarines without the Soviets finding out about it. That being said, Olavsvern, a submarine base outside of Tromso, Norway, is the closest thing to a secret submarine base. The base is located in the north of Norway, within the Arctic Circle.

Olavsvern was primarily designed to counter the Russian Northern Fleet, based out of Murmask a few hundred miles away. The base’s submarine pens are buried deep underground, because it was built into the side of a cliff, making it resistant to bombing.

Of course not. Submarine bunkers are an outdated concept from World War II. The Germans built huge impregnable U-boat pens in Germany, France and Norway that made it possible to for them to operate submarines in range of allied airpower. A few other nations like Sweden and Yugoslavia used them in later years because they were subject to surprise attacks from their location close to the enemy.

It is impossible to make something as big as a submarine bunker secretly. No sub could hide there, they were just protected from bombing there. The advent of nuclear weapons made the whole idea a waste of money and resources. They are too vulnerable, now.

The US in particular needs no secret submarine bases. The sub bases they operate are in very good locations that are very far from their enemies. The bases are in harbors protected from the ocean but have free access to the sea and subs don’t have to pass through straits controlled by other nations.

The US has no need to hide the existence of submarines from Russia. Their presence has a deterrent effect on US adversaries. Keeping them secret would not accomplish this. The US wants Russia to know that they can out-produce the Russians in submarines and once those subs are at sea they are impossible to track.

This is where the US hides submarines from the Russians—at sea. Bunkers are neither secret nor safe. They are sitting ducks.