So far I have found two site that give short overviews of how ASW works:
http://fas.org/man/dod-101/sys/ac/asw.htm
http://www.global-defence.com/2000/pages/antisub.html
I will try to put together the things that I have read or found out by playing Harpoon about ASW:
ASW(Anti-Submarine-Warfare) is a joint effort.
Ships,helicopters and planes have to work together to detect,attack and possibly sink a submarine.
Usually it goes like this:
A destroyer sails over the sea until all of a sudden it detects a faint noise over the towed arry (passive sonar).
That might be from another ship or perhaps a submarine,it will a take while to find out by comparing the sound profiles to profiles of known ships.
At that point only very little is actually known about the contact,only its bearing,signal strenght and with a little luck the class.
Not enough to fire a weapon at it.
No if the contact would be close enough (im talking of about 15km at best) then the destroyer captain might decide to send an active sonar ping to get the submarine exact location (range,bearing).
But in case the captain would have to be very lucky to so close to an enemy submarine,usually the submarine hear the ship first.
So lets assume the ship is to far off to take any action other than listen,off course the ship could come closer to the submarine but that would dangerous so either a helicopter or a plane to further pin down the contact.
The aircraft would then use active dipping sonar and drop sonar bouys to set up a kind of perimeter in which the submarine COULD BE.
Harpoon showed this process very nicely by showing an area that gets smaller the more accurate the contact gets.
"Digging out" the submarine is tedious process,it takes time and lots of sonar bouys get dropped.
All in all this takes a lot longer than detecting air or surface contacts with an radar even with the help given by the destroyer.
If a contact is detected by radar then you have the bearing AND the range,so you have the exact location in contrast to just a bearing in the case of an sonar.
Additionally acitve sonars (and those on sonar bouys included) have a much smaller ranges than radars.
One sonar bouy I have found information about had a detection range of about 0,4km.
So in order to pin down a submarine it would take a good guess and a good number of them to pin a sub down.
Yes a plane can set out to hunt submarines but it would have to have a good number of number of sonar bouys,just one or two dont make sense.
The P3 Orion carries 87 of them.
There is also the MAD (Magnetic Anonmaly Detection) which is a sensor that looks for disturbances of the magnetic field of the earth.
Disturbances caused by objects made of iron like submarines.
Great idea,but the plane has to fly more or less directly over the submarine and even if you get a contact it might still only be wreck.
So back to to Georges question:
Cant the planes and helos simply drop sonarbouys?
Yes of course they could!
But they would have to drop quite s few (especially if the are on their own in terms of sensors which the game assumes they are)
AND while they will then be capable of scanning the water they WONT have the spotting range they would have for detecting surface ships.
Their spotting range would be quite small for detecting subs,and Im not sure if it would be possible to implement different spotting ranges for different targets into the game.
And that whys I suggested to introduce the "detect sub flag" to ensure that only units with "dedicated ASW equipment" and an for ASW appropriate spotting range can find submarines.
