2009/05/25

ASW vs. SSK - the struggle will go on

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A few days ago I wrote about modern active low frequency sonars, bi- and multi-static sensor networks.

The raison d'ĂȘtre of these new technologies is to detect enemy submarines (even AIP SSKs) at a long range. Actually, at such a long range that the anti-submarine surface combatant will fire the first shot (and can avoid going into effective range of the sub).

Several such sonars were introduced, so we can expect them to meet the expectations (good enough range against SSK) at least today (likely with restrictions as usual).

It will take a few years till this is a topic in public discussions on ASW*, but then I expect to see a typical conclusion; some will conclude that the time for the submarine is over.
That would be strange - why would so many navies place such an emphasis on new submarines then (including the Australian Defence white paper calling for 12 SSK and the German navy investing in new AIP SSK even though it's a LF bi-static variable depth sonar user)?

The spiral of measures and countermeasures will likely just go on - only old and not yet upgraded subs will be obsolete subs.

The countermeasures can be grouped into (at least) four groups:
* reducing the chance of detection
* reducing the chance of identification (after detection)
* strike first with long range weapons on its own
* reducing the vulnerability to attack (after identification or chance attack)

What could we expect as countermeasures?
- a new coating that absorbs even LF sonar energy well
- acoustic cancellation technology / active noise control (may be impossible against multiple receivers)
- the use of static decoys (passive reflectors, reactive emitters)
- the use of jammers (may be pointless due to modern signal processing capabilities)
- the use of mobile decoys (unmanned underwater vehicles; UUVs) to saturate an area with false targets
- tactical exploitation of the underwater terrain to become less exposed to sonars
- the use of longer-ranged munitions (probably more emphasis on cruise missiles than torpedoes against surface targets)
- combination of arms; like fighters killing ASW helicopters
- sub-to-air missiles (the long attack range capability of ASW ships rests on the ability of their helicopters to carry lightweight torpedoes to the sub's area)
- ...

The German navy uses both AIP SSKs (Typ 212A subs) and LF bi-static sonars (Typ 123 frigates) and seems to be at the forefront of SSK/ASW technology. It's not surprising that it sees the need for a sub-to-air missile, one of the possible and publicly known countermeasures against ASW forces with effective long-range silent sub detection.

I'd like to point out something about the use of decoys; it may be possible to deploy enough and good enough decoys to make identification impossible. The defender would need to engage all contacts at long range - and have some means of observing the effect of the attack.
This costs a huge quantity of lightweight ASW torpedoes, a classic problem of ASW warfare since the Cold War. The U.S.Navy did a study in the 70's about the likely expenditure of lightweight torpedoes in a typical North Atlantic convoy scenario. The quantity of false contacts due to natural causes was such that the escorts would have run out of torpedoes before crossing the Ocean. The British experiences during the Falklands War kind of confirmed the results. They expended dozens of torpedoes and (afaik) it's still not known whether a single of the contacts was really an Argentinian submarine.

The USN concluded that its ships needed more torpedoes, and I assume that the expected high ammunition wastage was a major problem for high-cost ASW torpedo projects (like Mk.50). The value of large inventories of more affordable torpedoes (Mk.54) was obvious.
If only the fleet could recover expended torpedoes that were fired at false contacts - just as it's being done during exercises. More about that later.

There's a new round in the fight sub hunters vs. submarines, and this time the (newest) sub hunters seem to score better. This round won't last forever, though.

Sven Ortmann

*: The "submarines and all else are targets" view on subs and sub hunters is still strong and based on experiences with obsolete ASW technologies.
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3 comments:

  1. " at such a long range that the anti-submarine surface combatant will fire the first shot"

    A couple thing bothers me about this scenario, Sven. Lets say for arguments sake, the surface warship detects the sub first. The ONLY long range weapon carried is the helicopter, which is a single fragile hope flying a few hundred Mach, usually less, to defend your convoy.

    Against this it will have to contend with the submarine which is firing sub-sonic or even super sonic cruise missiles, some of which outrange the helicopter. Some also now carry anti-helo missiles, and certainly would in wartime.

    We were promised before WW 2 that "Asdic" had solved the U-boat threat. Wasn't as simple as all thought when you factored in weather conditions, or a sub in silent running, or whether you had enough ASW escorts, ect.

    You could be right that these new sensors will work as promised, but until the ASW community has a weapon to match or outrange the submarine's weapon, plus the stealth to match, then I will less worried.

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  2. Mike, my opinion in this text was much more complex than you depict it.

    The next big naval warfare text has been in preparation for weeks. It includes what could be called a solution.

    By the way; do you recall that the South Koreans invented the Q-pirates link scare to get their naval helicopters protected against IR-guided missiles?
    I considered that as necessary for years now, and that's not related to pirates. I believe the South Koreans have their reason (other than pirates) to call for such equipment, too.

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  3. Wouldn't it be nice to have a not-so-drastic sub weapon that messes up (maybe cuts, maybe destroys) the LF towed array without harming the ship?

    In general: The art is to have subhunters in the place where the subs are. If you don't have that, then even the greatest and latest technology you might own won't help. :-)

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