SSBN- A ballistic missile submarine is a submarine capable of deploying submarine-launched ballistic missiles with nuclear warheads. The United States Navy's hull classification symbols for ballistic missile submarines, SSBN – the SS denotes submarine, the B denotes ballistic missile, and the N denotes that the submarine is nuclear powered. (Wikipedia)
Personally, I sleep well at night knowing Tridents are manning the seas. Unlike bombers and land based nukes, they are our first and last defense against nuclear war. I've read that even the President doesn't know their locations at any given time, unless he needs to send the EAM to a nuke sub.