American Submarines carry 70% of U.S. present arsenal of nuclear weapons

The advantages of nuclear submarines is people don't usually know where they are. So, if America was struck by ANY country, soon that country would be dust from nuclear missiles from all U.S. nuclear submarines stationed at various places around the world at that moment.

ON PBS Newshour they are talking about replacements for nuclear submarines here in the U.S.
The cost will be about 1 billion dollars per new nuclear submarine (but about 100 billion when you add in the research to build one. So, they are talking about replacing them one by one with 1% of the defense budget for the U.S.

All this information was on PBS Newshour for Friday July 31st 2015.