[goldorak]

Originally Posted by Dr.Sid

Anechoic means it reflects less. But not nothing.

Yes of course, another thing is, the reflected ping doesn't have an isotropic propagation. Most of its energy goes into the direction between the emitter platform and the american sub. So any stray sub that wiould be out of this "axis" would not receive sufficient energy to be "visibile" on the american sonar. Do I have the physics wrong and the reflected ping instead would also be propagated isotropically, its energy being distribuited evenly in every direction ?

This method could work. Only problem would be that the 688 would be visible to the Chinese sub as well. Sure it all depends on geometry of the situation and sensitivity advantage.
But if the Chinese sub was close to the destroyer, it would be painted and visible, while the US sub could still be far enough to avoid detection.
On the other hand, if the Chinese sub was far away from the pinger, let's say slightly behind it's active range, it could pick the echo of US sub without being much exposed.

I'm still not conviced that a sub could be illuminated by this reflective ping if its position is way out of the line (bearing) between the chinese destroyer and the american sub.

Anyway, this approach would be better used with buoys. They can be passive (thus cheaper) and they you can use explosives or strong surface vessel to paint the area.

But those are interesting tactics. I wonder how much it is used too.

I think the 2 kinds of situations are different. In Clancy's description the us sub uses a ping generated by another vessel (an enemy vessel) to "paint" the area. But doing so obviously alerts the enemy units to the presence of the american sub, since the ping actually pinged on the us sub in the first place. Explosive echo ranging, and passive sonobuoys don't use a reflected ping to paint the area. The explosions generate the sound waves (equivalent to a normal ping) and then the sonobuoys simply listen to the echo.