The 87 foot WPB Replacement, an Addendum

The discussion on earlier posts, “The 87 Foot WPB Replacement –Response Boat, Large –Interceptor” and “57mm ALaMO Round” has prompted some additional thoughts that seem to require more than a comment, mostly regarding the 57mm Mk110 and its new ALaMO guided projectile.

I also had intended to mention the fact that, if the WPB replacement included provision for stern launch of an 8 meter over-the-horizon boat, as was done with the Webber class FRC, then any mission modules that might developed for the Webber class to take the place of the boat, as discussed in the post, “Webber class Could be the Navy’s Light Duty Pickup Truck,” would probably also be apply to the WPB replacement. These might include anti-ship cruise missiles, Unmanned systems, or small towed array sonar systems

While the Iran swarming boat attacks are the normal justification for developing the ALaMO round, the emerging threat, unmanned surface vessels (USV) used to make “suicide” attacks may have also been a consideration. As can be seen above, small fast unmanned surface vessels can be hard to kill, and they have proven an effective weapon as can be seen below. One method of attempting to deal with the swarming boat threat has been to have the projectile burst above the boat, showering it with shrapnel. These airbursts could work pretty well against manned boats by killing the exposed boat operators, but the technique is less effective against unmanned craft. It may even be possible to shield critical components of unmanned craft against the effects of shrapnel. This is also a threat the Coast Guard may want to consider since unmanned explosive motor boats are relatively easy to construct.

Video: Houthi attack on Saudi Al Madinah-class frigate using unmanned explosive motor boat. 

The new ALaMO projectile may have been developed with this Unmanned Surface Vessel (USV) threat in mind. This suggest to me that the projectile would be designed to home on the heat generated by the craft’s engine. This would work equally well against manned craft. If the ALaMO round is IR homing, then perhaps it would also home on the heat of a larger vessel’s engines as well, making it more useful for countering larger vessels. 

If the 57mm Mk110 gun’s projectiles have made it a reliable counter to small, fast, highly maneuverable threats and perhaps some midsized threats, and if it can discriminate between its intended target and other traffic that may be in the area, it may be worthwhile to consider its inclusion in the WPB replacement. I still do not see it capable of countering large or even many medium sized threats. I still think we need to know more about how the round works before we can assume this is correct, but assuming it is correct, can we put this weapon on a vessel this small? I think we can.

This brought to mind how some earlier craft that had had relatively large guns. I will discuss some of the them and point out what I believe were notable features.

Spica Class (Sweden):

Swedish Torpedo Boat T121 “Spica” Photo by Pressbild. “Tidskrift i Sjöväsendet”. 1966. November. Sid 595. Swedish and US public domain

If you look at the Spica class above, it is a bigger than the likely WPB replacement (139 ft loa and 235 tons full load, 40 knots, 12,750 HP). It is 2/3 the size of the FRC, and about 29% more than my assumed maximum (182 tons) for the WPB replacement. It was a steel ship. It was equipped with an earlier version of the same 57mm gun found on the National Security Cutter (NSC) as well as the 9LV combat system which was the basis for the Mk92 Firecontrol system used on the 378 FRAM, and six heavy weight torpedo Tubes. The Torpedoes each weighed approximately 1800 kilos or about two tons, while the gun weighted about seven tons, so the vessel had over 19 tons of weapons. The fire control,  ammunition, launchers, and Electronic Warfare equipment would have added to the payload weight. By comparison, if our WPB included the current model 57mm (16,535 lbs/7,500 kg), two Mk54 torpedoes (608 lbs/276 kg each), and eight Longbow Hellfire (108 lbs/49 kg) the total weight of weapons would only be a little over nine tons (18,615 lb/ about 8,461 kg) plus ammunition, launchers, Electronic Warfare equipment, and firecontrol systems. The Over-the-Horizon boat, a primary “weapon,” may add as much as four tons, so the full “weapons load” would be about 13 tons. (I could not find a weight for the Over-the-Horizon boat, but the larger Response Boat, Small weighs a bit over 8 tons.) That is about 68.4% of the weight of systems on the Spica. It is not a complete accounting, but I think it is indicative and I will continue to use this format below.

One thing I liked about this, and the next two designs, is that the bridge and operations rooms are located at or near the center of pitch (which seems to have been done with the FRC as well). This makes it more comfortable for the watch. It also results in a long foc’sle. This allows the gun to be well back from the bow while still being far enough forward of the superstructure to allow a wide arc of fire. That is, it is capable of firing well abaft the beam.

The Norrkoping Class (Sweden):

Swedish Norrköping class fast attack craft (missile and torpedo) HMS Ystad R142, 3 September 2010 Photo by Reedhawk

The Norrkoping class was derived from the Spica class and sometimes referred to as the Spica II class. It gained a little weight, being 143 ft loa and 255 tons (41 knots, 12,750 HP). Initially it was armed like the Spica class, but subsequently the four of the torpedo tubes aft of the superstructure were replaced by four RBS-15 missiles. These weigh in at about 800 kg or 1760 lb. Consequently the weapons load is almost a ton lighter than that of the Spica, but still over 18 tons plus ammunition, launchers, Electronic Warfare equipment, and firecontrol systems. At the same time the missiles were installed, the 9LV system’s radar was replaced by the Sea Giraffe which is the radar installed on the Independence class LCS and planned for the Offshore Patrol Cutter (OPC), US designation AN/SPS 77 V(1). This radar is also used on the Swedish Visby class corvettes completed 2002 to 2015. 

Willemoes Class (Denmark):

A danish navy Willemoes-class fast attack craft (missile + torpedoes) HDMS Sehested (P547) as a museum ship at the Holmen naval base. Photo by Flemming Sørensen

The Willemoes class were similar, slightly larger vessels (46 m/150 ft 11 in loa and 260 tons full load, 40 knots, 12,750 HP). Originally they were equipped with four torpedo tubes in addition to the Oto Melara 76mm gun. The after pair of torpedo tubes was replaced by launchers for eight Harpoon Anti-Ship missiles (1,523 lb / 691 kg with booster). Its weight of weapons after installation of the Harpoons was just over 15 tons, plus ammunition, launchers, Electronic Warfare equipment, and firecontrol system (also a 9LV).

The unique feature of this class was that they had small diesel engines for cruising at up to 12 knots.

The Storm Class (Norway:

The Storm Class, (120 ft loa, 138 tons, 30 knots, 7200 HP) is illustrated above, fully armed and launching a Penguin missile, and below in a later configuration after removal of missiles and transfer from the Norwegian Navy to Lithuania. It is considerably smaller than the vessels above, at the lower end of what I expect the WPB replacement to displace, but still capable of mounting considerable weaponry, in this case six Penguin anti-ship missiles, and 76 and 40 mm guns. The missiles weighed 385 kg (849 lb). The 40 mm weighed about 3.5 tons. I was unable to find the weight of this 76mm gun. It would not have weighed as much as the Oto Melara, but it has to be at least 6 tons, so a total weapons weight was at least 12 tons.

Lithuanian Naval Force, Norwegian built, Storm class patrol boat P33 “Skalvis”. Missiles removed. Photo by Ministry of National Defence Republic of Lithuania


If we chose to do so, it appears we could build something like a slightly scaled down version of the Spica that could mount a 57mm Mk110 forward and still provide an 8 meter Over-the-Horizon boat aft. The firecontrol could be as simple as the electro-optic unit from the Mk38 Mod2 or as capable as the SeaGiraffe which would give us a true all weather capability. In addition, it could probably mount tubes for two light weight torpedoes and eight Longbow Hellfire in vertical launchers. (I would think the Hellfires offset to one side, at the back of the superstructure. Foot print for a 2×4 cluster of missiles would likely be only about 4 x 3 feet.) I know the torpedoes are an unconventional approach, but it seems the surest way to stop a large ship and supposedly the Mk46 Mod5 and later torpedoes have an anti-surface capablity.

Replacing the Marine Protector class WPBs with vessels equipped like this would give the Coast Guard a robust and truly capable Ports, Waterways, and Coastal Security capability.



33 thoughts on “The 87 foot WPB Replacement, an Addendum

  1. What about the Tsurugi-class patrol vessel of the Japan Coast Guard?

    50+ knots on diesels and a Vulcan cannon.

      • Assuming you are referring to the Tsurugi-class patrol vessel,, would think it possible, but the Japanese CG has not done it. Instead, “In the Battle of Amami-Ōshima, the combination of the 20 mm gun with the RFS proved its worth, but it became clear that its effective range was insufficient against weapons on board the North Korean spy boats such as 9K38 Igla MANPADS and B-10 recoilless rifle. In response, the JCG intends to organize mobile flotillas combining Tsurugi-class with vessels of the Hida-class and the Aso-class, which have Bofors 40 mm L/70 autocannons.”

        The possibility of improvised armament on terrorist vessels is why I would like to be able to engage effectively outside 4,000 yards. Terrorists or state actors might arm a merchant vessel or fishing boat with machine guns, anti-tank rockets and missiles, old anti-aircraft and anti-tank guns, or recoilless rifles. Some of these weapons might have ranges greater than 4,000 yards but at that range they would be relatively inaccurate and unable to target specific parts of the cutter that would render it ineffective.

  2. Possible sensor fit option, relatively low budget.

    EO/IR – The Navy new L3 KEO’s MK20 Mod X Eletro Optical Sensor System, EOSS, weapon director & target search based on the Mk46 (Mod X said to be 60% lighter than Mod 0, and so able to be fitted higher on mast for increased range), a stabilized platform, daylight LLTV, a 3-5 micron mid-wavelength Infrared, MWIR, suitable for maritime environments (no mention of a shortwave infrared, SWIR, to enhance performance under foggy conditions) and an eye-safe laser range finder, accuracy to 30 microradian.

    Radar – Ultra Electronics Ocean Systems recently selected to develop and produce the Navy’s new navigation radar in a $28M contract, presume in reaction to the Burke 2017 collisions that resulted in deaths of 17 sailors. NGSSR will be a new two dimensional software defined surface search/navigation radar, to replace the AN/SPS-67, AN/SPS-73, BridgeMaster E series, and commercial-of-the-shelf radar systems in fleet.

  3. Here’s the thing Chuck, if were going to go the a same way as a FAC, I would say the Roussen class fast attack craft of the Hellenic Navy, the Ezzat class (Ambassador Mk III) fast attack craft of the Egyptian Navy, the Gumdoksuri-class patrol vessel of the South Korean Navy and the Hamina-class missile boat of the Finnish Navy would be somethings to base it off.

  4. You seem to be caught in the ‘weight – mobility – firepower’ trap. 🙂

    If you want a good seaboat and heavy weapons load out you are just going to have to accept bigger and that means more expense.

    The Japanese boat can always be upgunned; there is a lot of space back aft.

    What about the Super Dvora from Israel? Right length, good speed, and SPIKE NLOS?

    • The Super Dvora is an impressive boat, but it smaller than the Marine Protector Class. I think we will be looking for something bigger, in particular something that can launch a small boat, preferably the Over the Horizon boat.

      I am a fan of the Spike NLOS missile system particularly when attached to the Typhoon Remote Weapon System that is the Mk38 Mod2/3 in US service.

      The Japanese boat is in what I believe will be the size range of the WPB replacement but it is not in any way exceptional that I can see.

      Don’t really see that I am in a ‘weight – mobility – firepower’ trap. It appears we could provide what I believe is adequate armament on a patrol boat of 182 tons or perhaps a little less.

      • I think you are looking at 250 tonnes for what you want in terms of sea keeping, weapons load out, and speed. Anything less than 200 a real squeeze.

        I think somebody has already suggest the 250 tonne Hamina-class. That’s the closest fit……..

      • Well Chuck, if your in the ‘weight – mobility – firepower’ trap, I suggest looking at the Turkish Navy’s Tuzla-class patrol boat, the other is the Gumdoksuri-class patrol vessel from South Korea or Australia’s Cape-class patrol boat.

      • Of course in the contracting process the Coast Guard would not specify a displacement, they would simply specify the capabilities necessary and we would see what was offered.

        Frankly I see the Hellfire and torpedoes as more important than the 57mm and it is a relatively costly addition compared to a Mk38 remote weapon station. But if the new round makes it as effective as advertised, then it might be worth doing.

        Remember that the weapons are paid for by the Navy.

        I do think the additional capability might justify some additional displacement and even the Hamina’s 250 tons is still only 71% of the displacement of the Webber class. Still the Haminas (, which I think are an amazing combination of capabilities for its displacement) do have several things, in addition to the 57mm gun and fire control, that we probably do not need, that might allow a lower displacement. The Hamina class mounts eight Umkhonto Anti-Air missiles, each weighing 130 kg or 290 pounds, four RBS-15s (a relatively heavy anti-ship missile at 800 kg or 1760 lb. or about 3.5 tons total). It also has electronic warfare systems including chaff, rails for mines or depth charges, and Simrad Subsea Toadfish sonar and a Sonac/PTA towed array sonar (weight unknown but probably enough to offset the additional weight of the boat for the cutter).

        Really I would not mind if the cutters ended up larger, 200, 220, or even 250 tons if they get funded and end up with the ability to forcibly stop ships of all sizes.

        There is an interesting note on the planned updates to the Hamina class, The 57 mm gun will be transferred to their new corvettes and be replaced by a 40mm/70 Mk4. Torpedoes will be added, initially Torped 45 (, later Torped 47 ( These are Swedish built light weight torpedoes that are a bit larger than the USN light weight torpedoes being 400mm diameter as opposed to the US 324mm, and they incorporate wire guidance as well as homing technology for use against both surface and submarine targets.

  5. If you put systems on a PB replacement which turn the rqmt into a FAC(M), there will be issues.
    First the Navy will want to take over the program. Second it will grow in size and weight such that only a dual-service ship will be authorized.
    You need to stay within the FIAC(M) type I think?

    • I am not sure how loading this much weaponry on a WPB will leave any weight/space for other missions? Particularly migrant interdiction or cruise ship rescue, where there will be a need to take on tons (literally) of passengers. For interdiction, this is even too much firepower.

      Rather than packing on firepower for firepower’s sake, I’d rather see weapon systems with specific purpose for the mission. I know this is where Chuck started with his basis on the ALaMo round, but I’m not sure we’ll see USVs or suicide boats in coastal US waters… I’d rather see the development of a wire-guided, acoustic-homing lightweight torpedo for the Webber replacement. Other than that, a Mk.38 and a .50-cal should do all that’s needed.

      • The way looking at our smaller cutters, I see it the Webbers are going to be the primary alien migrant interdiction vessels. The WPBs would be primarily SAR response craft–the real FRCs.

        Neither WPBs or WPCs is going to be able to handle a cruise ship sinking. That would require an all hands on deck, AMVER response of the entire local maritime community.

        As discussed before I think we can conceptualize the terrorist threat as two extremes of a spectrum of vessels, (1) small, fast, highly maneuverable boats, and (2) medium to large merchant vessels. If we can handle those extremes then we can probably handle all threats.

        I don’t feel comfortable relying exclusively on guns with unguided projectiles since they can cause significant collateral damage, put our units within range of improvised weapons on the terrorist craft, and are probably inadequate to reliably stop larger vessels.

        So I look to small missiles to take out the smaller threats and torpedoes seem the best system to forcibly stop the larger threats. Those systems don’t have to take up a lot of room or weigh a lot, but so far the Coast Guard has shown no interest.

  6. JMSDF Hayabusa-class patrol boat? Just under 250 tonnes, about 50 kts, missiles, 76mm gun…..

    ….but 3 GTs instead of 4 diesels. I prefer the latter.

    • Whatever the gun chosen for use by the Navy and CG, it should have at least some anti-air capability. I think this says more about the mount, sensors and ammunition available than the gun itself but it is worth mentioning. The “system” should have at least some anti-air capability.

      We are in the age of the drone where even non-state actors can seemingly launch drone and anti-ship missile attacks against “soft” targets.

      As the technology proliferates and matures, this will only become more of a threat.

      Once again, not trying to convert our cutters into Kirovs, just give them a better chance of survival if caught in the wrong place.

      Dual purpose systems that do not impose too much overhead on the ship seem the way forward.

  7. Just realized, perhaps these should be designated Maritime Security, Small, WMSS. We already have large (NSC) and medium (OPC). Makes it sound more like a Homeland Security project.

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  10. Some interesting designs in this category here

    33 M VERY FAST PATROL BOAT and ARES 125 look interesting.

    and here

    FAST ATTACK CRAFT (FAC 42) and Fast Attack Craft designed by RMK Marine

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  13. Another WPB being decommissioned, without direct replacement. Only reference to replacement was, “The Coast Guard commissioned four 154-foot fast response cutters in California between 2018 and 2019, which operate along California’s entire coast and international waters off Mexico and Central America conducting missions such as search and rescue, fishery patrols, national defense and port, waterways and coastal security. ”

    This is a location where the new larger class of MLB would be a good replacement for a WPB.

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