Following a number of collisions this year with civilian vessels which resulted in numerous deaths, the US Navy has begun broadcasting the locations and journey plans of some of its ships.
The broadcasts which can be tracked along with thousands of other civilian ships will only take place when the US Navy ships are in waters that have high volumes of traffic, particularly around major port cities and routes. This follows after two major collisions, first with a merchant ship, and second with an oil tanker, that happened to the USS Fitzgerald and USS John McCain, respectively, and resulted in 17 dead in total.
The broadcasts are deactivated once the ships reach open or less crowded waters and would probably be deactivated at times of war. You can currently watch the USS Chaffee on its journey to Pearl Habour or find other vessels if you type US Gov into the search bar at marinetraffic.com; it is quite astonishing to get an idea of the number of ships there are at sea right now.
Recently we learned that US submarines would start using Xbox 360 controllers to control their periscopes; being able to find and track US Navy vessels is a lot of information and news from an organization that is usually, for good reason, quite secretive.