Thresher/Permit class submarine

The Permit-class submarine, originally known as the Thresher class, was a class of nuclear-powered fast attack submarines (hull classification symbol SSN) in service with the United States Navy from the early 1960s until 1996. They were a significant improvement on the class, with greatly improved sonar, diving depth, and silencing. They were the forerunners of all subsequent US Navy SSN designs. They served in the 1960s through middle 1980s, until retired due to age. They were followed by the and classes.