There was a thread started on this yesterday...here is my take on this.
The destroyers don’t just trail those things along for no reason (I am a brown shoe, so any of you SW types out there who know ASW better than I do can comment on it)
They have a cable that is more than a thousand feet long (I don’t know how much more) it is maybe an inch in diameter, and the array at the end is VERY expensive. Knowing how those things are, they don’t just put them in the water for a swim unless they were doing an exercise, and to have it just randomly hit a Chinese sub...well, the odds would be very long indeed.
My understanding of the Chinese sub fleet is that the numbers of platforms are limited, equipment is okay, not great, and the crews haven’t spent a lot of time at sea. I read that their entire fleet did twelve patrols in 2008, which is a lot more than any previous year. Last I heard, they did six in one year, and had a few years they only did one or two.
It is possible that our military is keeping an eye on the Chinese subs now the way we did with the Soviet subs. We try to pick them up on satellite as they leave port, track them with hydrophones as far as we can, then they are handed off to ASW planes and surface ships that keep tabs on them. This is just a guess.
My take on it is that the folks aboard the USS McCain knew that sub was **somewhere** out there, was trying to pin it down and ended up dragging their array right across it.
People are correct in that a decent modern diesel electric boat is a very significant threat indeed. But my guess is that lacking blue water capability, replenishment vessels and such is that this was not the case. In the absence of those things, the diesel subs are better suited to littoral roles. I’ll bet it was one of their nuclear subs.
Again, my knowledge of this is from talking to S3 guys when I was in and what I have read, all unclassified stuff which has been worked into biographies and novels.
I was an ASW officer many moons ago. The towed array sonar is a passive sonar, that listens only. They were certainly aware of the presence of the Chinese sub, but would not have had an accurate range. The towed array would have to be baffled to mask the towing ship’s signature noise. Perhaps, the Chinese attempted to hide in the “baffled” zone, and miscalculated it’s postition, since it’s sonars were also in passive mode.