USS Nautilus hull material context

Now the US Navy does it for nuclear submarines, but nuclear submarines are sort of a different matter. It's a 22 billion dollar vessel, and you tend not to like to lose them. I try to keep track of them, find out where they last docked and things like that. It's not like losing your keys, but almost. People keep on wanting higher and higher toughnesses. Is that really necessary? Well, there are some reasons why it might be. For example, when I worked for the steel company, they were building LNG tankers — these great big steel ships that have great big aluminum spheres, five of them, like five stories tall or five stories wide, these big aluminum spheres. In order to hold that sphere you have to have a cylinder that you put the sphere on, and that was made out of steel, and that had to have toughness at minus 60 degrees Fahrenheit.