There have been several
recent articles about the LCS ASW module being overweight and how it’s not
really a problem and what amazing new capabilities the module will bring to ASW
warfare. Of course, the module consists
of technology that’s been in use for years so it’s kind of hard to figure how
the module will bring amazing new capabilities but that’s not the point of this
post. Further, the Navy assures us that
modules diet plan to lose weight is not a problem. Of course, the weight issues have been known
for years and, presumably, the Navy has been attempting to lighten the module
for quite a while now and this is the result.
This version is, one assumes, the lightest version that the Navy could
assemble over the last couple of years of effort while still maintaining the
requisite capability. Thus, it’s hard to
imagine where significant additional weight loss will come from without cutting
into capability but, again, that’s not the point of this post, either.
Setting the preceding aside,
the main component of the ASW module, such as it is, is the Thales CAPTAS 4 variable
depth sonar (VDS) or a similar variant. This, according to
the Navy is an amazing piece of technology that will allow us to accomplish ASW
feats never before seen. Of course, the
Thales VDS has been around and in use by foreign navies for years and the US
Navy never before deemed it worthwhile.
Kind of makes you wonder, doesn’t it?
Be that as it may, if the
VDS can add capability that’s a good thing.
What is it that makes the
VDS useful over a conventional hull-mounted sonar, anyway? Well, as the name implies, the VDS can be
raised or lowered to any desired depth, somewhat akin to a helo’s dunking
sonar. This allows the sonar to listen
under thermoclines. Thermoclines are
temperature gradients in the ocean that form layers. The layers tend to reflect sound at the
boundaries between layers. Thus, sound
at a lower layer can be trapped or channeled within that layer and not
propagate to the layer above or below it.
A submarine can hide in a lower layer that a surface ship’s sonar can’t
effectively penetrate. Hence, the value
of a VDS is that it can be lowered into a lower thermal layer and detect a sub
that a ship with just a hull-mounted sonar can’t.
Which, again, begs the
question, why hasn’t the Navy pursued VDS systems before? I have no answer for that. The old Soviet ships had VDS but I have no
idea to what extent, if any, they were used.
Moving on … Does the VDS bring with it any drawbacks or
limitations? As you might suspect from
the question, the answer is yes.
The first limitation is that
the VDS requires around 20 minutes to deploy or retrieve. Thus, the LCS can’t just hop around the
liquid battlefield, nimbly racing to and fro collecting data. Instead, it’s going to have to carefully pick
its spots with the knowledge that once it commits to a spot, it will be there
for an extended period.
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| Thales VDS |
This leads to the second
limitation and that is the vessel’s speed while the VDS is deployed. The LCS was predicated on speed, speed, and
more speed (not sure why but the Navy assures us that speed is critical). Unfortunately, the VDS only functions at very
low speed and, therefore, the LCS is limited to very low speed while the VDS is
deployed. Higher speeds will not only
negate the VDS performance but may damage the unit if towed at too high a
speed. This presents a bit of a
dilemma. If the VDS is deployed and a torpedo
is detected, the LCS can’t use its speed to escape. It becomes a relatively immobile target. On the other hand, if the LCS chooses to retain
its speed capability, it can’t deploy the VDS and, thus, won’t be able to hear
a sub or torpedo. Hmm … That’s a real Catch-22: use the VDS and forfeit speed or use speed
and forfeit the VDS. The LCS can’t have
both.
Presumably, the Navy has
already made the decision that the VDS is more important than speed or else
they would not have pursued the VDS option.
Of course, that leads one to wonder what use the Navy foresaw for speed
in the first place. But, I digress …
If the Navy is committed to
using the VDS extensively, that implies that the LCS is no longer removed from
the ASW battle. Sonar performance in
littoral waters tends to be short range.
Recall that the original LCS ASW concept called for remote unmanned
vehicles and vast underwater sensor nets that would be deployed and allow the
LCS to stand off from the actual ASW battlespace. So, with the LCS now conceptually committed
to up close and personal ASW battles, we have to wonder about the LCS’
suitability for such a role. Lacking the
built-in quieting that a purpose-designed ASW vessel would have and operating
noisy waterjets would seem to put the LCS at an enormous tactical disadvantage
in ASW operations.
All of this leads one to
wonder how carefully the Navy thought out the revised ASW module concept. Has anyone gamed out how a loud, speed
impaired LCS with no ship-mounted ASW weapons will fare in an ASW battle? I strongly suspect that the answer is no and
that a lot of sailors will pay the price to find out that the LCS is unsuited
for ASW work.
The VDS was a knee jerk
reaction to the abject failure of the original ASW module and was not well
thought out. The Navy has to start
thinking ahead and ensuring that they have logical and viable concepts of
operation before jumping into development paths that make little sense.
