It appears that anyone can start tracking US Navy vessels online whenever they are traveling through congested waters:
Naval enthusiasts are tweeting what they believe are U.S. warship positions after commanders ordered the vessels to activate their beacons while in congested waters to avoid collisions.
The order to turn on the Automatic Identification System (AIS) locators, reported by National Public Radio on Sept. 29, follows a series of collisions that have killed 17 sailors in the Pacific in recent months.
However, it appears that the new procedure is also allowing people to track the warships online.
A tweet posted on Sunday that maps the location of a “US GOV VSL” approaching Hong Kong reads: “Reason to believe this is USS Ronald Reagan (CVN 76).”
The aircraft carrier and the guided-missile destroyer USS Chafee anchored near Hong Kong on Monday, a Pacific Fleet statement said. [Stars & Stripes]
You can read more at the link.