The hope is to only use passive sonar to detect an enemy. It's like using your radar in a fighter plane. If you go active it gives away your position long before you can detect the other guy. You want to use sensors that don't radiate, or at least don't radiate in a manner that puts you at risk. That's why working with an AWACs is so successful for fighters. They know where the bad guys are because the AWACs tells them, but the bad guys can't detect them. Of course, they can detect the AWACs so they know someone is out there, and you have to detail some folks to protect the AWACs, but you get the idea.
From what I understand we should be able to detect these boats just fine when they're operating. The concern is that they'll get into position at a strategic choke point before our forces get within detection range then just sit totally quiet waiting for us to get in range. That requires different capabilities and tactics.
Also, I don't think these are accurately called "diesel submarines." I believe they are diesel/electric submarines. They operate on battery power when submerged and surface (snorkle) to run the diesels to recharge the batteries.
We need some bubble heads to chime in and correct my semi literate notions.
I'm not a bubble head, but I have a few friends that are.
I believe you are correct that this is more correctly termed a diesel/electric. It would be pretty hard to run a diesel underwater for an extended period of time. The diesel is used for surface running and to charge the batteries.
Subs are very easy to track when they are running the diesel. As you noted, they are very difficult to find when they are sitting still.
I'm no submariner, but you've got it pretty good.
In simple terms, that's sort of what the LFA program is about...a remote active platform.
So that's what AWACs are all about. Thanks for the info.