August 3, 2016

China's current SSBNs Limited - Thermoclines little help - Part Two

As argued in Part One (August 1, 2016) compared to the open ocean (where SSBN commanders prefer to operate) the South China Sea is restrictive.

China's SSBNs might possibly be sent, from their main Yulin/Sanya/Hainan Island Base, north to operate in the protected East China Seas or Yellow Seas. But movement north would put them in closer range of Japanese and South Korean SSKs and Russian SSKs and SSNs. Very quiet, experienced US SSNs (that can range far and fast) might be the main hazard for Chinese SSBNs.

If a Chinese SSBN wanted to break out of these restricted waters into the wider Pacific Ocean it might move east through the gap between Northern Luzon and Kyushu (Japan's most southern main island). But this would put the SSBN further away from the protecting Chinese air force. And also the the SeaWeb undersea array (see the Map above) has been intentionally laid by Japan and the US between Luzon and Kyusho to detect just such a submarine breakout attempt. Noisy Chinese SSBN signatures would be easily picked up. 

To make life even more difficult the SeaWeb sensors can be positioned in restricted waters so as to be just below a Chinese SSBN's maximum diving depth and above it.


People sometimes think that if a submarine dives deep enough it can take advantage of the major change in water temperature (thermocline) by sitting safely below the layer. This would be correct and comforting to the submarine commander if the sensor threat were only on the surface. 

Problems occur for the SSBN if the enemy can deploy gadgets that can get TO (or are below) the sub's protective thermocline layer. These gadgets-tactics include:

1.  an ASW surface ship's towed sonar array ("Picture 5:" below) which is most likely to be set deep
     (say 300 or 400m sonar). 

2.  long dipping sonars from helicopters that can suddenly appear. Like towed sonars, dipping sonars
     may well "active" - hence able bounce off the hull and detect even subs that are hardly moving.
     An SSBN switching its reactor to silent mode, while using battery powered thrusters, will not
     totally hide it from active sonar. 

3.   sonobuoys dropped in a pattern, in front of the sub's likely path and set to reach the same depth as
      the sub

4.  seafloor arrays (sitting on the black line at "Picture 5:" above) or tethered sensor arrays can be
     usefully laid for long term use in restrictive waters (like the Yellow Sea, East China Sea and South
     China Sea). Or, in addition to sonobuoys, they could be laid (especially air-dropped) on a shorter
     term basis in front of the likely path of the SSBN.

Diagram 1 courtesy USN 2006. A seafloor array, called "Fixed Surveillance System (FSS)" is neatly described in U.S. Navy Program Guide 2015 (large PDF 6 MB) which explains, on page 128:  "...FSS comprises a series of arrays deployed on the ocean floor in deep-ocean areas and strategic locations. Due to its long in-situ lifetime, it provides indications and warning of hostile maritime activity before conflicts begin. The system consists of two segments: the integrated common processor (ICP), which handles the processing, display, and communication functions; and the underwater segment, which consists of SOSUS, a long array of hydrophones,.." . 

So this US openness on seafloor arrays feeds China's concerns over Chinese SSBNs having to operate  in restricted waters. Concerns came to a head in 2009 when US sonar survey ship USNS Impeccable operated just 75 miles south of China's Yulin/Sanya/Hainan SSBN Naval Base. Chinese aircraft and naval militia boats buzzed Impeccable constantly and quite understandably. 

The chances that Impeccable was dropping seafloor and tethered sensors were real, bothering the Chinese and it still bothers them. 



Anonymous said...

This current submarine-warfare-setup which favors the West (SK & JP as allies) over China - even if we count in advancement in tech on both sides.

So this China with only ONE option: The return of Taiwan into the fold.

Let's assume a democratic-legimitated CPC-dominated China manages to bring Taiwan peacefully back into the fold sometime in 2050s.

The first major movement of the PLAN would be setting up major naval-bases on the Eastern coast for the boomers. This will allow them dive into the Pacific straigt away. Alternatively the Bastion-strategy with the Taiwan Stait - blocked in the northern and southern entrance.

Furthermore IN,PHL,VN and TH are not small flies. If they get act together, their combined naval strenght will give the South Seas Fleet a run for their money - if the economic projections are true.

All the West has to do is to sow discord between China and its' neighbours, but not too much.

Team Eurowussies

Josh said...

The problem with the Yellow or East China Seas is that they are far more shallow than the SCS, the Yellow in particular to the point of limiting operations to periscope depths in most places. There isn't a known satellite EO, IR, or SAR detection system capable of detecting a boat or its wake from orbit but the worry would always be there at such shallow depths. Some Sino defense sites have commented on the problem of the most deep water access port, Hainan, still having a 100 mile run to deep water for any sub. For SSKs this likely also involves snorting.

Impeccable is a SURTASS vessel and its activity is probably limited to directly listening for/to submarines via towed array* and not laying sensors (though that is a possibility). Sensor laying is more likely done by TARC-7 Zeus or USS Jimmy Carter. Alternatively some types might be air deployable**. The Chinese interest in Impeccable was probably 1). making it go away and 2). attempting to capture its towed array for reverse engineering.

The Chinese operate at a distinct disadvantage in that on top of having a very land locked patch of water to work with, they also have to deal with the most sophisticated naval power already being on their doorstep the moment they seriously entered the ASW game. They have no room to train or test without observation. They understandably get a little miffed at patrol craft. Life is tough all over.

*I believe TAGOS-23 specifically uses a 'twin line' version of the TB-29 which can optionally work along with an variable depth LF active emitter suspended below the ship.

**The USN has experimented with buoys that are self powered by wave action; it wouldn't take a huge leap to make a moored sensor that had independent power and communicated by satellite. The Iridium constellation is known to have been used as a radio access gate in Sea Web tests.


Nicky K.D Chaleunphone said...

Hi Pete,
This may Interest you from Defense news

Taiwan Establishes Submarine Development Center

Peter Coates said...

Hi Team Eurowussies

In my next article, out tomorrow, I will quantify the regional and US submarine forces, pitted against China.

If the other undersea sensors of SeaWeb are also considered - even if the PLA-N built an SSBN base on the east coast of Taiwan it would only be a marginal improvement over the PLA-N current geographical and technical limitations.

More likely China needs to await a more general US withdrawal from all US bases in East Asia. This is probably talking the year 2040+ when the Chinese economy starts to equal or surpass the US economy in size.

With US withdrawal Taiwan will more likely be absorbed peacefully rather than being the focus of a pointless WWIII.

I understand up to a million Taiwanese live and work in mainland China. The numbers of Chinese in Taiwan with close family connections on the Mainland must also be high.



Peter Coates said...

Hi Nicky

I think if Hillary wins Taiwan can expect continuation of NO US political, technical or financial help for a submarine project.

If Trump wins, the field is wide open under his blank piece of paper foreign policies. The Trump Plan may involve:

A. US help for a Taiwanese sub project OR

B. Trump may make a deal with Mainland China to cede Taiwan to the Mainland.

The people of Taiwan live in interesting times.


Peter Coates said...

Hi Josh [at 4/8/16 3:39 AM]

For some reason your email comments have been going to SPAM – best to put “Pete” on the top.

The East China and Yellow Seas are indeed too shallow for relaxed Chinese SSBN sailing. The depth map shows those seas are mostly shallower than 200 meters. This depth deficiency provides a sound reason why China has opted to place its SSBN in the South China Sea based (South Sea Fleet) area.

Aircraft can drop sonobuoys (with some operating on the seafloor and/or using tethers So I don’t think many different surface vessels would have any trouble lowering or dropping sensors, SURTASS or not.

I don’t think the USN would miss an opportunity just because a vessel has one main function written on the Ship’s Log.

Impeccable’s catamaran-twin hull design also expedites covert lowering of seafloor sensors (under the “arch”) away at least from the prying eyes of surface ships, aircraft and satellites.

I’ve indeed written about

There seems steadily less need to lay actual cables (the specialty) because smart sonobuoys/sensors can form communications networks using underwater wireless radiocommunications link frequencies and/or very long term underwater hard-disk memories (sensors 1/00 or 1/1000th the size of Ivy Bells with a memory a Billion times greater)

Agreed - even in the Indian Ocean the Chinese cannot test their subs without looking over their shoulders. Also, notably, there have been no maximum range (8,000 km(?)) JL-2 SLBM flight tests.

Yes can be totally self-powered and or nuclear batteries have been used (away from people) for some time.



Josh said...


I would expect a permanent wired system would exist with few to zero unwired stand alone sensors. In the case of crisis or war, additional semi-permament/medium term systems would be delivered covertly by sub or rapidly by air, along with the normal short term buoys we're all familiar with. The stand alone censors would provide additional coverage area and act as a backup in case cabled systems were disabled (cable cutting or by missile attacks on their processing stations). The semi-permanent system could report directly to CONUS via satellite as a back up to any local control node or alternatively add to the local system.

Cables allow for a steady power supply and instant unjammable communications with near unlimited bandwidth for raw data to go directly to shoreside processors. Stand alone systems need to 1). generate or store their own power, via long term battery, wave action, solar, RTG, etc. and 2). are limited generally to burst communications either through acoustic modem or low bandwidth satellite. This means a lot more in buoy/sensor processing has to be performed and that communications are much slower, less reliable*, with much less transmitted information**.

The other thing to consider is that any of these systems could potentially be recovered by PLAN operations as has been done before (mk46,mk48,attempt on SURTASS), so likely the most sophisticated stand alone sensors would not be deployed to prevent them from being compromised before a crisis or conflict. Cabled sensors can skip the technological hurdle of acoustic and SAT comms along with the sensitive and high tech task of signal processing. They can be more or less at the same tech level as civilian acoustic or magnetic sensors used for oil exploration and send their raw data through high band width cables (where cuts and breaks can be detected) and all the high tech signal processing and associated algorithms can be secure in a friendly country or US territory.

I've seen an old RFP that involved acoustic modems, magnetic sensors, hydrophone arrays, and a central long lasting power source packaged together in a single store that roughly equates to a mk46 body which I assume would facilitate P-3/P-8 delivery. Of course its impossible to say if anything ever came of this.

*Seaweb communications tests were never 100%, and even when they work the speed of sound plus the need to carry the message across numerous underwater nodes to a radio gateway makes transmission far less than instant.

**A stand alone sensor must process all of its own raw data into a target picture. Easy enough for say a sub, much harder for a sonobuoy - normally raw data is generally fed to the aircraft and the aircraft's systems and operators interpret it.


Peter Coates said...

Hi Josh

Thanks for the comment.

I'll revisit wireless sensor issues (including sonobuoy networks) in ten days time.