2009/06/09

Sub vs ASW ship: The range mystery

.
I wrote about the new Russian frigate class recently, and there's something that keeps irritating me. Maybe it's justified by obscure operational analysis, but why exactly have even relatively new ship-to-sub missiles such a limited range?

The RPK-9 Medvedka (2nd link) (to be used by the Russian frigates) and the RUM-139 VL-ASROC both are believed to have ranges of little more than 20 km (I'm not in the mood to think in nautical miles today).

RPK-9 Medvedka (Russia): 20 km
RUM-139B VL-ASROC (USA): 22 km
These ranges likely don't include the range (about 10 km) of the payload; a lightweight anti-submarine torpedo.

The heavy submarine torpedoes (much slower, of course) are believed to have ranges like 40-60 km.

YU-6 (Chinese): 45 km
Mk.48 ADCAP (USA): 50 km
Torpedo 2000 / Tp62 (Sweden): 50km
Black Shark (France/Italy): 50 km
Seehecht M2A4/Seahake Mod.4 (German): 50 km
Spearfish (British): 54 km
These ranges depend on batteries. Old torpedoes could have degraded batteries and therefore lesser ranges.

No matter what the real (and effective) ranges* are; let's temporarily stick to the assumption that the publicly available specs are for real.

The range disadvantage would be no major problem if the torpedo attack was detected early on open seas, as the target could speed away from it. That would work just fine for (usually fast) warships (depends on how early the warning was, of course).
That's a rather optimistic scenario, though; early warning, high speed and the necessary freedom to maneuver out of range cannot be taken for granted.

Another excuse would be that submarines cannot acquire sufficient target information at beyond the ASW missile's range to risk a shot (that might give away their presence). That's possible, but would often be untrue. SSKs in ambush positions near a coast could expect external targeting assistance (airborne radar data, radio data link). It's furthermore not a safe assumption that the ASW ship will detect the sub at a longer range than it will be detected by the sub. That's possible, but likely very dependent on the situation.

Another problem is that a submarine in a blocking position could easily repel an entire enemy fleet if the fleet is avoiding to enter the sub's weapon range. Such dances end sometime, and that's when ships (or subs) will be sunk.

The standard ASW method of attack would be the use of helicopters to deliver lightweight torpedoes against the submarine (after confirming its position with the helicopter's sonar systems).
That approach is in my opinion unreliable. I expect lightweight anti-air missiles on submarines in wartime. That's a top candidate for a secret capability; a strong requirement and a huge benefit of keeping it secret.
There were several disclosed projects for such weapons , including the ongoing IDAS missile project.

The heavyweight torpedo vs. ASW missile range comparison yields many uncertainties, but there's another irritating comparison possible:

The sub-to-ship missile vs. ship-to-sub missile range comparison.
Anti-ship missiles can be fired from submarine torpedo tubes with assistance of a special capsule and a booster.

SM39 Exocet (France): 50 km
UGM-84D Harpoon (USA): 140 km
P-800 Oniks (Russia): 150 km
3M-54 Klub versions (Russia): up to 300 km

These missiles are much faster than ships. This reduces the ship's speed to a question for the missile's terminal homing capability and pretty much deletes it out of the missile range question.

Again, the question of confidence in the firing solution arises; can a submarine make good use of such ranges?
Most certainly not without external assistance. The first few kilometers range advantage over ASW missiles are what interests me, though. A sub-to-ship missile that can reach just 10 km farther than a ship-to-sub missile constitutes a huge weapons range advantage.


Finally there's the story of the UUM-125B ASW-SOW "Lance" missile. It was meant to replace ASROC to offer a greater range, but got cancelled due to budget reasons in 1990.
There was a requirement for a longer-ranged ASROC equivalent in the 80's, and I'm sure budget reasons didn't change tactical considerations. The Lance is a strong hint that there's likely indeed an ASW range problem.

- - - - -
It seems to me as if the anti-submarine capability of modern frigates depends too much on fragile and somewhat weather-dependent helicopters. It's even more irritating that the Russian ASW FFG design apparently has only hangar space for a single helicopter (or, as some sources assert; only a landing pad).

It's usally a good idea to diversify, to have more than one asset to address a problem. A single, apparently fragile and not fully reliable asset (ASW helicopter) does not convince me as a single asset against the formidable challenge of SSKs.
Some ASW ships don't even use an anti-submarine missile and depend almost entirely on helicopters to kill subs. The production run of VL-ASROC (apparently only 450) wasn't big anyway.

My concept for a future naval battle fleet was in part designed to avoid this problem with a screen of small units that are usually unworthy targets for a sub (not worth to risk compromising the sub's own location with a first strike). These screening boats were meant to have heavyweight torpedoes (the same as used by subs).

The publicly available anti-submarine missile ranges make no sense to me. They're either wrong or many ASW ships have some quite questionable ASW weapons onboard.


*: I strongly suspect that they cannot match the range of the sub's anti-ship weapons.
The combination of payload torpedo length+weight, propulsion type and overall missile weight indicates that even SM39 Exocet is likely longer-ranged than ASROC.

Sven Ortmann

edit 2009-06-12: It seems as if the Americans see the need for longer range. I missed this apparently rather new proposal for a glide wing kit-enhanced VL-Asroc. Again, a hint that we've got a technical insufficiency in our ASW equipment at present.
.

10 comments:

  1. Some thoughts on ASROC range: I am not a submarine guy, so please bear with me. I would expect that the heavy torpedo range does not matter that much because

    a) torpedoes usually aren't shot in a straight line, and can be set up to run many different attack scenarios; think cruise missile and way point navigation; and

    b) a slow sub (chasing another slow sub) and shooting a slow torpedo needs to cover quite some distance with its weapon because the target is moving away; that's not so for ASCROC since it moves much faster and the figthing happens quicker.

    Then c) I believe ASCROC and the like might be of particular value in shallow and confined waters with difficult sonar conditions, where both sides are operating in a fog situation and might end up being much closer to each other than usually desired by a surface ship.

    Finally: I am curious what is possible in terms of distance when it comes to reliably identifying a (passive) sonar contact. A sub is not likely to receive high quality position and identification data based upon radar, SIGINT or airborne reconnaissance. So even if a contact might be in range, you wouldn't know if it is the right one to spend an expensive torpedo on.

    ReplyDelete
  2. I think I already addressed (b) indirectly.

    Passive sonar target identification is based on target sound profiles. You listen to ships at peacetime and catalog them, so you'll recognize classes (and possibly even individual ships) by their sound profile in wartime.
    Well, unless Murphy's Law is in effect.

    ReplyDelete
  3. Sure, any frequent watcher of modern sub movies :-) knows about sound signature databases.

    But: I very much doubt that "I hear something" is identical to "I know what it is" let alone "I know _who_ this is". And the "where exactly" is yet another question.

    ReplyDelete
  4. As far as peacetime signatures, I would bet that some subs have peacetime and wartime emission modes.

    As far as firing solutions, unmanned drones and unemanned underwater vehicles are the best (and cheapest in material and labor) option for the future.

    ReplyDelete
  5. if a ship detects a torpedo attack early it can outrun it. from my calculation the minimal range at which a adcap can no longer outrunned is slightly less than 20 km. (assuming straight running)
    in this case a sub is within the asroc range. you may call it a optimistic scenario because it needs early warning but if you can not detect a torpedo attack at a range of 20 km you don't need a asw missile with a greater range because you are not able to detect a sub at this range and you can't shot at something you can not detect and track.

    asw warfare isn't a question of weapon range, it is a question of sensor range. that's the reason why asw helo's are so useful. they can dispense sonobuoys quickly and they can dipping around. the sensor ranges are limited but they can repositioned in a very short time.

    ReplyDelete
  6. There are additional factors.
    Torpedoes depend on wire /fibre-optic cable datalink till their terminal homing phase.

    Imagine a torpedo launch was detected late. The sub is at missile range +1 km and it's too late to outrun the torpedo.
    There's no way how to engage it to force evasive maneuvers (breaking the wire) or to even destroy it before the torpedo enters terminal homing distance to its target.

    The simple high speed torpedo run scenario isn't the most interesting because the range is reduced very much by high speed (and high speed is noisy).

    The Lance project with its long range is in my opinion an indicator for a larger range requirement than ASROC's.

    I cannot play through all relevant scenarios in a tiny blog post. The subject is large enough for a dissertation (as too often).

    ReplyDelete
  7. The Russians also have the 91RE2 ASW missile. It can be launched from the same VLS as the Onix SSM. It has range of 40 km in its export version.

    ReplyDelete
  8. Yes, I overlooked that in the confusing variety of the Klub family of missiles.

    "The supersonic 91RE1 (long) and 91RE2 (short) types are anti-submarine missiles, armed with a 324mm self-homing torpedo. Both types go ballistic after launch, directed to the target area via INS. Their ranges are 50 and 40 km, respectively."
    http://warfare.ru/?catid=312&linkid=2181

    ReplyDelete
  9. The South Koreans announced such an ASW missile, specs are unknown to me.
    http://www.koreatimes.co.kr/www/news/nation/2009/06/113_47231.html
    "more than 20 km"

    ReplyDelete
  10. Couple of thoughts--

    While heavy weight torpedoes are uncommon on Western escorts the Krivaks and several other classes of Soviet escorts carried heavy weight torpedoes.

    Ship vs Sub is seldom one on one. ASW done right is a multi-unit exercise. While the reliability of one helicopter might be problematic, in a force that includes 6 to 12 helicopters it is less of a problem. The Japanese seem to have this figured out very well with four standing ASW groups of eight ships, one DDH (starting to look like light carriers), two AEGIS, and five other ships.

    If the helo is you primary ASW weapon, then the missiles and over the side torpedoes are viewed as quick response weapons to be used when you are surprised by finding a submarine nearby.

    I do also see that sending a missile could simplify getting a target solution when all you have is a fleeting contact beyond direct path in a convergence zone. Getting a solution for a torpedo requires estimates of course and speed that would not be required for a missile. This looks to be more to the surface TG's advantage than the subs, because the sub reveals its position by firing a missile, that isn't an issue for the ships.

    ReplyDelete

Use a nickname and stick to it! I may block anonymous comments. Offensive comments may also be blocked, in part due to the duties of a blogger in Germany.