Chinese Sub Collides U.S. Destroyer's Towed Sonar Array

[Straha]

In what a U.S. military official calls an "inadvertent encounter," a Chinese submarine hit an underwater sonar array being towed by the destroyer USS John McCain on Thursday.

The array was damaged, but the sub and the ship did not collide, the official said. A sonar array is a device towed behind a ship that listens and locates underwater sounds.

The incident occurred near Subic Bay off the coast of the Philippines.

The official, who declined to be named because the incident had not been made public, would not say whether the U.S. ship knew the submarine was that close to it.

However, the Navy does not believe this was a deliberate incident of Chinese harassment, as it would have been extremely dangerous had the array gotten caught in the submarine's propellers.

The Navy has complained in the past that Chinese vessels, including fishing boats, have deliberately tried to disrupt U.S. naval activities in international waters near China. In one widely publicized incident in March, five Chinese vessels maneuvered close enough to the USNS Impeccable to warrant the use of a fire hose by the unarmed American vessel to avoid a collision. The Navy later released video of that incident.

[Venator]

I suppose that's one way to stop them from tracking you on sonar...

Realistically, though, I'm puzzled as to how easy/hard it would be to avoid/hit an array like that. Would the array be pinging actively or just using passive sonar, and what kind of depth do they run at?

[TimothyC]

I suppose that's one way to stop them from tracking you on sonar...

Realistically, though, I'm puzzled as to how easy/hard it would be to avoid/hit an array like that. Would the array be pinging actively or just using passive sonar, and what kind of depth do they run at?

1. The Arrays are Passive

2. The Russians did this back in the cold war, and it is a known way to steal a towed array.

[Ma Deuce]

Realistically, though, I'm puzzled as to how easy/hard it would be to avoid/hit an array like that. Would the array be pinging actively or just using passive sonar, and what kind of depth do they run at?

All towed sonar arrays are passive only: they're basically just a very long cable (in this case almost 2 km) with hydrophones attached at various points along their length. For surface ship arrays, the depth of the end of the cable would depend on the ship's speed and how much of the array is deployed, but would generally range between 150 to 450 meters down.

[Fingolfin_Noldor]

Realistically, though, I'm puzzled as to how easy/hard it would be to avoid/hit an array like that. Would the array be pinging actively or just using passive sonar, and what kind of depth do they run at?

All towed sonar arrays are passive only: they're basically just a very long cable (in this case almost 2 km) with hydrophones attached at various points along their length. For surface ship arrays, the depth of the end of the cable would depend on the ship's speed and how much of the array is deployed, but would generally range between 150 to 450 meters down.

I think the Ocean surveillance ships such as the Impeccable employ an active towed array to emit long wavelength sound pulses.

[Ma Deuce]

I think the Ocean surveillance ships such as the Impeccable employ an active towed array to emit long wavelength sound pulses.

Checking...yes it seems you're correct about SURTASS being active, and there are apparently a small number of other arrays now produced by other countries (such as CAPTAS) that have an active capability as well. Of course in this case, the array was passive-only.

[Tanasinn]

Is it too much to hope that they're being sent the repair bill?

[Themightytom]

There's a destroyer named after John McCain? Thats kind of awesome for him. What are navy rules for naming ships if anyone knows..

[Rogue 9]

There's a destroyer named after John McCain? Thats kind of awesome for him. What are navy rules for naming ships if anyone knows..

The destroyer is named for his father and grandfather, both naval officers; the senator is John S. McCain III.

[Sea Skimmer]

The active component to SURTASS is added through a second array used in conjunction with the original passive only set. IIRC only one of the survilliance ships has the new active array so far, but plan is to put it on all of them, as well as all destroyers and cruisers which will be retained for more then a couple more years.

[Pelranius]

Wouldn't it have made sense to turn on the active sonar if the passive sonar detected the Chinese sub (direction is nice, but distance is just as important)?

The last thing the USS John McCain needed was for the PLAN submarine to cut off and run away with part of the sonar array.

[TheLostVikings]

Wouldn't it have made sense to turn on the active sonar if the passive sonar detected the Chinese sub (direction is nice, but distance is just as important)?

The last thing the USS John McCain needed was for the PLAN submarine to cut off and run away with part of the sonar array.

Why did you get the impression that they detected it at all before the collision? Modern subs are almost too stealthy for their own good, like the collision with the french sub a while ago, they simply didn't detect each other before they hit.

[Ma Deuce]

Wouldn't it have made sense to turn on the active sonar if the passive sonar detected the Chinese sub (direction is nice, but distance is just as important)?

What makes you think passive sonar can't be used to determine distance?

[JointStrikeFighter]

Wouldn't it have made sense to turn on the active sonar if the passive sonar detected the Chinese sub (direction is nice, but distance is just as important)?

What makes you think passive sonar can't be used to determine distance?

A towed array makes it even easier to detect range passively because you have two [or more] listening sources and can thus use trig to work out the range.

[Venator]

Thanks for the info on the array - I was thinking that it might run on active because a surface vessel doesn't get to play stealthy in the first place, unlike a sub. If it was only listening, though, I can understand it being much harder to detect (assuming it was an accidental collision on the Chinese's part).

[Thanas]

Thanks for the info on the array - I was thinking that it might run on active because a surface vessel doesn't get to play stealthy in the first place, unlike a sub. If it was only listening, though, I can understand it being much harder to detect (assuming it was an accidental collision on the Chinese's part).

Surface vessels get to play stealthy and are in fact designed to be as stealthy as possible.

[Raw Shark]

Is it too much to hope that they're being sent the repair bill?

"Yeah, our bad. We'll knock it off your tab." -China

[Venator]

Thanks for the info on the array - I was thinking that it might run on active because a surface vessel doesn't get to play stealthy in the first place, unlike a sub. If it was only listening, though, I can understand it being much harder to detect (assuming it was an accidental collision on the Chinese's part).

Surface vessels get to play stealthy and are in fact designed to be as stealthy as possible.

I meant relative to a submarine; I know that modern ships have a lot of stealth[y] technology in them, but a ship has the distinct disadvantage that you can see it.

[Pelranius]

The problem with visual identification is that the sub also puts itself at risk of visual and radar identification by coming up to periscope depth, if you're talking about actual eyeballing of the ship.

It's possible to soundproof a warship to reasonably high standards, but it's probably just more cost effective to invest on measures for finding the enemy sub rather than hiding from it.

[Sea Skimmer]

The problem with visual identification is that the sub also puts itself at risk of visual and radar identification by coming up to periscope depth, if you're talking about actual eyeballing of the ship.

A modern submarine isn’t likely to put the scope up for more then about a literal second at a time; it’s very hard to detect that even with an active radar set. You can put up the scope, confirm you have spotted a godless American infidel, and put the scope back down before the radar can complete a sweep (literally, dodge between radar pulses). Specialist periscope detecting radars exist, but most ships don’t have one. Lookouts aren’t a huge threat just because modern ships don’t tend to have very many, while back in the World Wars a single cruiser might have as many as 24 dedicated lookout men, and several officers to do nothing but supervise them. However modern ships do have electro optical turrets rather like the ones you find on targeting pods or attack helicopters. They can spot periscopes, and are also used to ID targets for gunfire. But such a turret can only look one place at a time. The odds of looking at the right piece of ocean at the right second are not good.

Anyway, if the ship has radar going then the submarine could also put up an ESM mast while over the horizon and get a bearing on the target ship without that ship ever even having a chance to detect it in turn. Submarines tend to have very high quality electronic warfare setups for that purpose. They can also home in on things like the ships radio chatter with its anti sub helicopters. Those ESM masts are also really useful for collecting intelligence in peacetime.

It's possible to soundproof a warship to reasonably high standards, but it's probably just more cost effective to invest on measures for finding the enemy sub rather than hiding from it.

Those two things are directly related. The more noise a surface ship makes the worse its own sonar will work, and even the sonar of a helicopter or another ship several miles away will be affected. This is part of the reason for towed arrays, they let you tow the sonar anything from 2-5,000 feet behind the ship and get it away from your own noise. The better the sonar works the more likely you find the enemy first.

The British Type 23 frigate is the best example of a stealthy (in sonar terms) surface ship. It was powered by diesel engines for cruise. Normally a diesel is very noisy, the worst possible thing in fact as diesel submarines are notorious for how much noise they make.

However by using an electrical drive system the British could put the diesel engines far above the waterline in the superstructure, and in this position (plus a high level of rafting) they radiated very little noise into the water. The screws themselves were turned by small low power electric motors.

When high speed was needed, for sprint and drift tactics, Type 23 still had a pair of gas turbines which could be activated, and were directly attached to the screws through a gearbox. They also had rafted machinery and all the noise reduction features you’d find on a contemporary SSN, though Pararie/Masker system took the place of rubber tiles on the hull.

Disadvantage was by placing engines above the waterline they became highly exposed to missile and air attacks, and raised the ships center of gravity. The US SURTASS ships have a somewhat similar setup (but diesels only, no boost gas turbines) but nothing else I know of does. Everything is about building multirole ships now, and the trend is to invest most ASW capability in a ships helicopters. Networking also helps ships with not super awesome sonar performance be more effective now.

[Glass Pearl Player]

Wouldn't it have made sense to turn on the active sonar if the passive sonar detected the Chinese sub (direction is nice, but distance is just as important)?

I can think of counterarguments: First, if you start pinging all of a sudden, the other guy knows that you know that he's there, and can make deductions about your passive sonar performance (and start thinking about evasion, if you were hunting him). Second, due to the r^2 vs r^4 problem of passive vs active sensors in general, everybody else in the general area knows where you are, and probably from ping characteristics, who you are. Third, if your sonar crew has any competence, they already have a good idea about range by something called Target Motion Analysis. Think of it as the art of triangulating a moving target with a single sensor (yes, that can be done). Fourth, every time you ping you announce your sonar specifications to anyone listening. Fifth: Every time you ping, God kills a dolphin. Think of the dolphins!

(and the fuzz the PR department will raise as soon as Greenpeace learns of it)