I was a sonar technician on two nuclear powered submarines in the United States Navy, the USS Florida (SSBN-728) and the USS Asheville (SSN-758).
Here is the Navy's official FAQ on submarines, containing everything you wanted to know but were afraid to ask.
Here is a picture of some stuff from my short time in the Silent Service. Pictured are my silver dolphins, the National Defense Service Medal, the Good Conduct Award, the Battle E, my submarine qualification card, my certification from the USS Florida stating that I am Qualified in Submarines (I am also qualified on the Asheville), and a plaque from the Asheville.
Though difficult to read in this picture, the CO's inscription on the photograph on the left states, "19 September 2000. Seaman [my last name] -- Congratulations on your qualification in submarines! Welcome to the band of undersea warriors."
Things are intentionally blurred and blacked out in this image to respect people's privacy etc.