Bluebulb Projects' The Measure of Things presents:
680 is about nine-and-a-half times the number of Submarines in the US Navy.
In other words, the count of Submarines in the US Navy is 0.110 times that amount.
(a.k.a. Subs) (includes all types, all classes) (2015 figures)
The United States Navy maintains a fleet of 72 active submarines. A typical submarine goes to sea with a crew of about 140.