Bellman, in a multistation dive recently, with darksythe and MaHuJha (full AAR to be posted soon if not already) we came out of sprint less than 5nm from an Akula II that had bottomed itself and was waiting in ambush, already having fired a torpedo at us.
It fired on us while we were running blind at 20kts and when we came out of the sprint, the torpedo was already tracking us 45 degrees of the bow at 2.5nm. We immediately turned hard left and headed due north and dropped two active decoys and snapshot down the torpedo bearing.
When we counterfired, the Akula II put anothre torpedo in the water, very accurately. The first torpedo's lock was actually broke by our torpedo counter shot, that gave us enough time to get behind our decoy screen, and the first torpedo acquired the double decoys and ran past us. The second torpedo had us dead on so we cut back to the south west and dropped another decoy, this one just confused the torpedo enough that it ran directly between us and the decoy, missing our sub by less and 100m (probably closer to 50m) and ran right by.
The bottomed Akula II couldn't get going in time and we gave her the old rapid decompression death.
So decoys are effective under 5nm, you just have to be on your game, as Molon said.
