Only one. She was a contemporary of the Nautilus. It was their experience with that vessel that killed liquid metal coolant for the navy. It might help to un

Only one. She was a contemporary of the Nautilus. It was their experience with that vessel that killed liquid metal coolant for the navy. It might help to understand something special about the nuclear navy in those days - prototypes in the lab don't count. Prototypes on land don't count either. The only prototypes that counted were ones that actually went to sea. All the way through the Skipjack generation, they were regularly doing crazy-eyed one-off experiments. Nautilus and Seawolf were both prototypes.