Monday, June 10, 2019

LCS IR Signature

Signature reduction was a major part of the Freedom variant LCS design and the slanted shape of the hull and superstructure is testament to the attempt by the designers to reduce the radar signature of the vessel.  How well they succeeded is unknown.  Beyond vague descriptions like, “a radar return the size of a fishing vessel”, there is no actual radar signature data that I’m aware of.

Another important aspect of signature reduction is infrared (heat).  Let’s take a closer look at this.

The first aspect that jumps out is the pair of diesel exhausts located on the ship’s sides, just above the waterline as seen in the photo below.  Note the discoloration around the exhausts.  On a side note, the various ‘camouflage’ schemes (it’s not really – it’s just a crew ‘feel good’ paint project) that have been applied to the ships all make a point of painting dark black around the exhausts as a means of hiding the exhaust stains.

Diesel Exhausts Low on the Hull, Marked by Stains

Diesel Exhausts Covered by Black Camouflage Patches

From a combat design point of view, the location of heat sources, in the form of the diesel exhausts, near the waterline invites hits by heat-seeking missiles at the waterline which is the worst place to have a hit as hits in that location have a high probability of causing flooding damage.  Given the LCS’ minimal manning concept and survivability design intent to abandon the ship upon receipt of a significant hit, placing heat sources at the waterline all but guarantees the hits will be significant and the ship will be lost.

The one unknown aspect is whether the diesels would be operated in combat.  The diesels are used for ship systems power and can be cross connected to the main propulsion system, as well, so I assume they would be operated in combat but I don’t know the combat power management scheme so I can’t say for sure.  If the diesels are not used in combat then this is not a vulnerability.

The other source of heat is the exhausts from the ship’s turbines.  For the Freedom variant, four 750-kW Fincantieri Isotta-Fraschini diesel generators provide 3 MW of electrical power to power the ship systems, according to Wiki.  For newer Freedom variants, Fairbanks Morse has been selected to provide two 16-cylinder Colt-Pielstick PA6B STC diesel engines that will deliver 12 MW of propulsion power. (2)

Note the location of the main exhausts, circled in the photo below.  From a combat design perspective, this is problematic since the exhausts are located within 20-30 ft of the ship’s main radar, the TRS-3D/4D.  Thus, a hit by a heat-seeking missile on or near the main exhausts will almost certainly destroy the ship’s radar which provides the targeting for the ship’s only air defense, the short range AAW missile defense RAM launcher.

Main Exhaust Location Near Radar

The exhaust location, essentially, invites the destruction of the ship’s only AAW defense.

This post is somewhat speculative in that I don’t have any data on the ship’s actual IR signature but it’s not much of a reach to believe that the main exhausts and the diesel exhausts, if they’re used in combat, are the primary point heat sources.  As we noted, the location of the main exhausts relative to the ship’s radar is problematic.  For a ship that was supposedly designed with significant signature reduction in mind, the main exhaust location is puzzling and suggests a design philosophy that is not focused on combat.  As noted in many other posts, this tendency to design warships without a focus on combat is as well entrenched as it is misguided.  All of this is just one more bit of proof that the LCS is not, and cannot be, an effective combat vessel.


(1)Naval Technology website, “US Navy’s LCS 4 completes main engine light-off”, 29-Oct-2012,


  1. Lovely paint job. The Visby class corvette that you've mentioned before solved this by releasing exhaust fumes in the water line creating a very characteristic cloud around the ship adding to its ocular visibility.

    It is also interesting to note the number of antennaes, guns and other bits and pieces sticking out of the Freedom class. Are these peace time equipment or will they remain in case of war? Again comparing to the Visby class, the difference is striking.

    All wartime antennaes are hidden in the top cone. The main gun is enclosed in the turret. The railings will also be removed.

    Wether or not it is all worth it I don't know. But it looks like the designers didn't go to the same school.

  2. On a somewhat related note, this last week was Fleet Week here in Portland, OR, and the Navy made an appearance with USS Pinckney (DDG) and the USS Independence. Although I wanted to get aboard and chat with the crew,weekend work schedule only allowed a brief driveby with some of my kids. Interesting thing, after giving them a rundown of the ships purposes, capabilities, etc, even teenage girls were able to determine that the LCS design lacked many "proper warship" elements, and they even questioned "whos idea was that to build somthing without a real plan?"... They were much happier with the Burke, as it was "probably able to do somthing it was built for..."
    The location of the exhausts on the Freedoms is a bit odd. Extra holes in the hull, especially in engineering spaces, is never a good idea! Even near miss/shock damage could invite flooding.
    To be fair though, theres only so much you could do to separate the radar and the exhaust. Is there any kind of exhaust cooling on these ships to help mask the heat?

    1. " theres only so much you could do to separate the radar and the exhaust."

      Actually, there's a lot you could do to gain separation. For example, swapping the location of the 30mm gun pits and the main exhausts. There are several ship classes around the world that have their exhausts located at the stern and/or underwater. Main exhausts could have been routed out the sides, high on the hull. There are actually lots of possibilities! I'm not a naval ship designer so some of my ideas might not be practical but the point is that there are lots of options. The LCS designers were clearly not thinking combat when they designed the ship.

      I've always been intrigued by the idea of an extreme stern location for the exhaust. Combined with a small area of heavy armor, a hit there would result in much of the explosive effect being directed out over the water instead of the ship and a small armor transverse bulkhead would further isolate the effects from the ship. Just my amateur attempt at a combat design.

    2. I understand your points. My comment wasnt a solid statement, but a generality in that you normally just send the exhaust "up"... And while possible, rerouting exhaust from the vertical could eat up large volumes of hull/superstructure, and I think moving them too far aft could create problems with flight ops. All speculative of course... The fantail exhaust seems a good idea, the loss of internal volume being the only downside...

    3. Another detractor being that light damage could potentially fill compartments with exhaust and make them uninhabitable until repaired being another...

    4. Yet another approach is the USS Kennedy, CV-67, which had canted exhausts which discharged out, away from the island and landing area.

      Between the current designs around the world and the history of ship design which has seen nearly every type of exhaust location and method possible, there are many workable options. The LCS designers opted for the most conventional and least combat-appropriate.

  3. HAA! You gave me a good laugh with the photos, COMNAVOPS. I don't remember the LCS 1 ship design having any serious nod towards signature control/reduction, but I would need to "go back in time" and look at the guidance the shipbuilders were given. First comment above was on the correct line with the thought about all of the topside clutter. From an RCS standpoint, hit Alpha will come where the white domes are, those cylinders are pretty perfect radar reflectors. And they guarantee that the CO will get to say "Hi" to the incoming missile homing on RCS because they are right above the bridge. My laugh came from the pic showing the main exhausts. look at the gray antenna just aft of the exhausts (one of two onboard, and those domes are actually shaped to reduce RCS). Covered with soot, and a guaranteed pain in the keester for some poor schmuck who has to clean it after every underway. So he/she's not laughing, but this is what happens when you just throw stuff up there "aftermarket". I know the thought process was "Fleet says I need this comm system to be a useful asset, not much topside room, OK put it THERE (in the exhaust gas path of the main engines)," and now, we have screwed the crew. Valid point on IR/heat. If the designers were serious about that it would have been managed, from the pics, looks like it was mismanaged.

    1. Mismanagement is the nickname for the LCS Zummies Fords F35 dang near all the current generation of weapons and ships

    2. Directions to the builders are constrained by cost!

      A $300 gold wedding band is going to be plated.


  4. A simple question as I dont really have a idea but aside from NSM what other ASHMs have IR guidance aren't mist radar guided

    1. There's a bunch: Penguin, Maverick, NSM, LRASM, several Japanese Type xx, SS-N-22 Sunburn (Moskit), Turkish SOM, SS-N-2, etc.

    2. DM Lewis: Technically, the IR guidance on Penguin, Maverick, NSM, and LRASM is IIR - Imaging Infra Red, as opposed to heatseeking IR ala Sidewinder missile. You've got a thermographic camera that sees an image of the target and flies towards it. It's not attracted to heat in the conventional sense, but because it sees an IR image, it's less susceptible to flares. This is where the theoretical use case for laser point defense comes in: less to totally destroy the missile, and more to blind the guidance system so the missile doesn't hit what it can't see.

      Manufacturer's claims for NSM and LRASM say that since the missiles have a threat library in their heads, you can blindfire the missile at a set of coordinates, it will use the radar seeker to pick up targets, and compare the image the IIR seeker sees with the threat library to 1) identify targets on its own and avoid civilian shipping and 2) identify and attempt to attack optimal points on an enemy warship. This, however, strikes me as a very, very fanciful idea, given the issues machines have with visual identification.

  5. Have the Navy re-learned any lessons from the failure of the LCS classes.

    From the various video interviews given by Ret'd VAdm. Rick Hunt at SNA and SAS2019 (Chief Strategy Officer for Fincantieri Marinette Marine), on their FREMM contender for the FFG(X) contract, Hunt said Navy has emphasized reduction in acoustic, infrared/heat and RCS signatures.

    Noticeable from pics the Fincantieri FFG FREMM design compared to Italian FREMM has a lower top side superstructure which will reduce its RCS which has the side benefit lowering the top weight by installation of the three panel EASR/SPY-6 (V) 2 radar in deck house at low level (downside lowers the radar sea surface horizon level range to spot incoming sea skimming missiles) should result in lowering height of the CG and require less ballast to improve intrinsic ship stability and SLA, sea life allowance for future weight growth margin.

    Though Fincantieri may have made design changes to reduce the infrared/heat signature Hunt made no mention in interviews, assume FREMM has by the far the lowest acoustic signature of four remaining contenders for contract as original FREMM hull design was for ASW with silenced DGs with electric drive.

    To make it compliant to Navy survivability standards Hunt said they have toughened the ship, by adding several hundred tons of steel to hull to make it stronger, stiffening the bending moment, improving seakeeping and improving its ability to take a hit, also its hull ~ 22' longer at 496' (Burke IIA 509').

    1. And we still have Zero idea what the Huntington Ingalls design looks like

  6. The LCS has the perfect stealth profile: no one will bother sinking a ship that is neither a threat in combat or a source of resupply. By Not sinking an LCS our opponents tie up our manning, supply, and maintenance yards on an that could otherwise support actual combat vessels. If they sank them by the droves we might replace them with actual fighting ships. The only way the Chinese will waste a missile is if the IR signature matches a Burke, then might hit one by accident.
    Incompetent design and purpose is the perfect stealth coating.

  7. Hard to believe bit today's USNI has a article about Congress Finally getting tough on LCS only 10 years and 20 some odd ships Too Late


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