Let me explain further in term of Signal Intelligence.........(SIGNIT)
There are basically 2 discipline of Intelligence gathering.
Passive and
Active.
While passive does not mean you are literally doing nothing and active does not actually mean you are doing something (Well, actually it does, but you know what I mean) Those are the only intel gathering method available to any country.
The best way to describe active and passive intel gathering is the word "Intrusive" if an active gathering is under operation, you will physically intrude into enemy space and sovereignty.
Active Intel Gathering usually involve Army Special Forces, Spies, Aerial Recce. Which the intended method are conducted in a way to challenge the target sovereign integrity.
Active Intel Gathering may be used against non-belligerent nation, i.e. no active war may ever declared. Some of the most famous of Active Intel Gathering mission including Photo reconnaissance during Cuba missile crisis, U2 spy plane flew over Soviet Russia, or the combat intelligence on whereabouts of Osama Bin Laden and the rescue of Jessica Lynch.
Passive Intel Gathering on the other hand is an "Non-Intrusive" method for intelligence collection. By means of staying out of the target sovereignty, usually outside someone's airspace and territorial waterways. The advantage of Passive Intel gathering is immense, where you can literally conduct espionage
WITHOUT the risk of ever going to war or the loss of Intel gathering vessel (Either ships or airplanes). However, ones must have strong ELINT/COMLINT ability and equipment to conduct Passive Intel gathering otherwise they cannot conduct such operation with such distance.
Usual method are by Listing Post on-board ships and aircraft, also with satellite. Famous incident such as the attack of USS Liberty, the collision of EP-3C with Chinese PLAF fighter, and the USS pueblo incident in North Korea.
I perfectly understand what "passive" mean here. You do not need to be technical here.
I do not think u.s. ships are simply in passive mode in collecting intelligence information while in thousands of miles away. It is your personal "un-fracking-believable" :rofl" understanding problem.
You cannot conduct Active SIGNIT ops while you are thousands of miles away, Active mean intruding into Chinese sovereignty, I hardly think you can call a place where ship passes thousand miles off your sea coast is still Chinese water.....
You can only do passive intel gathering with ship that far.