In response to the four collisions American 7th Fleet warships have had during 2017 (and 17 sailors killed) in September the U.S. Navy ordered its ships to completely (broadcast and receive)turn on their AIS (Automated Identification System) when travelling in congested waters. AIS was originally developed to make it easier to track ships at sea and was rapidly adopted by most large commercial vessels in the 1990s. AIS is essentially an automatic radio beacon (transponder) that, when it receives a signal from a nearby AIS equipped ship, responds with the ship's identity, course, and speed. This is meant to enable AIS ships to avoid collisions with each other. The original AIS only had a range of 20-35 kilometers but by 2006 space satellites were developed that could track AIS transmissions worldwide.
The U.S. Navy adopted the policy of using AIS in “listen only” mode when overseas, especially in potentially hostile waters. American warships monitored AIS transmissions around them but obviously did not show up on the AIS monitors of nearby commercial ships. American destroyers are built to be “stealthy” (difficult for radar to detect) and that meant in congested waters commercial ships would concentrate on the other large commercial vessels in the area that were quite easy to track via radar and AIS. Until recently (the last 5-10 years) American warships devoted a lot more time and effort towards training sailors on bridge watch (who took care of navigation round the clock) to handle these conditions. This training was important because the average age of warship sailors on bridge watch was in the mid-20s while sailors on larger commercial vessels were much older and had a lot more experience at sea. The 7th Fleet, and the U.S. Navy in general, had responded to heavier workloads (because of tensions with China and North Korea, plus the War on Terror) by letting the bridge watch training system (and training in general) deteriorate. This was kept quiet, or least out of the mass media, until recently and for that reason it came as a surprise when senior officers in the 7th fleet were openly blamed for complicity (and relieved) for this situation. The U.S. Navy is now going through a leadership and training shakeup as well as more realistic attitudes towards maintenance and deployment schedules.
One quick response to the situation was the order to turn on AIS transmissions for warships in potentially dangerous situations. That makes these warships less stealthy but as the number of accidents (and near misses) in 2017 demonstrated this was preferable to more collisions and loss of life (usually to the warship crews). Besides the warships in question are already operating close to shore and in crowded waters, which makes it difficult to be hidden from any local navy. Commercial ships have become very dependent on AIS, which has greatly reduced collisions (and crew anxiety) at sea. After 2000 international agreements mandated that ships larger than 300 tons, and all passenger ships, carry and use AIS at all times.
While this made it practical to track all high seas commercial traffic, it was also exploited by smugglers and pirates. Some ships travelled (in violation of international law) with its AIS and other trackers turned off. Usually only criminals turned these devices off, and this was often discovered when navies spot one of these silent (AIS not broadcasting) ships at sea. It didn’t take long for some intelligence agencies (those with ocean surveillance space satellites and lots of ships and subs at sea) to exploit the “silent AIS” ploy to create better ways to track smugglers by noting when some ships turn off their trackers and then turn them on again as they are about to enter a port (or some other area where AIS use is mandatory). Some nations, like Iran and North Korea have cargo ships that are often found “running dark.” Naturally intelligence agencies developed methods to take advantage of this and a growing number of smugglers, usually North Korean, are detected and tracked because of AIS manipulation.
Before AIS came along most large ships carried (and still carry) INMARSAT, which enables shipping companies keep track of their vessels, no matter where they are on the planet. INMARSAT became available in the 1980s and uses a system of satellites which transmit AIS-like signals to anywhere on the oceans. It only costs a few cents to send an INMARSAT signal to one of your ships, and a few cents more to receive a reply. The trackers and satellite based navigation systems in general soon proved invaluable by prevent collisions or running into reefs, rocks, or (in bad weather) coastline.
The smugglers soon responded to intel agency tracking of AIS activity with new tricks. Back in 2012 Iran was caught hacking AIS signals. Iran was sending false AIS signals to assist its smuggling operations. After 2012 security researchers found even more ways to hack AIS and is calling for changes in the AIS software to make more difficult to spoof (send false signals).
Apparently Iran has been working for some time to come up with ways to confuse the international ship tracking system. These “maritime security technologies” were developed as a safety feature and have proved valuable in other ways as well by providing the positions of ships caught in storms or taken by pirates. All ships now use GPS coordinates to record location and constantly report that back to the home office. Iran exploited this by having two of its ships trade INMARSAT IDs while they are near each other, leaving the U.S., or anyone else checking INMARSAT data, unable to track ships that have been switched. Well, for a while at least. Once the intel people caught onto this scam the developed ways to counter it.
Because these tracking systems were, after 2000, required by law (international agreements) for all sea going vessels this new tech was particularly useful in counter-terror operations. Coast Guards the world over have also found the systems a big help. But apparently pirates in some areas have gained access to the systems (via bribes or theft) and a large number of pirate attacks appear to have been helped by technology meant just to safeguard ships at sea. But overall the tracking systems have done far more good than bad.