Novel Gun Mount


NavalToday has a short piece on the new German F-125 frigate. It is primarily to show the video above, of the frigate firing its 27mm guns and 5″/64 Otobreda.

The unusual aspect of the video is the way the mounts for the 27mm guns lean out (see 1:25). I’m not sure it is worth the complication, but it does permit the gun to fire at targets close alongside near the waterline. It probably means it can be fired on bearings closer to the bow and stern too.

Thanks to Mike R. for bringing this to my attention. 

New 40 mm Gun

Thales RAPIDSeaGuardian CIWS Euronaval 2016 newsThales RAPIDSeaGuardian Naval Gun System

Navy recognition is reporting the announcement of a new 40mm naval gun system, based on an existing land based system (pdf). It is claimed to be “a new generation CIWS effective against super sonic seaskimming missile thanks to the airburst ammunition, as well as against asymmetric threats…” while having about the same “footprint and weight as a 25mm system.”

The system is interesting, but the star of the show is the gun and its innovative ammunition. The ammunition is “Case Telescoped” meaning that the shell is embedded in the casing and surrounded by the propellent. The gun and its ammunition are products of CTA International, an equal-shares joint venture company between defence companies Nexter (France) and BAE Systems. The resulting round is very short and shaped like a cylinder rather than the typical double tapered shape of most fixed (one piece) ammunition.


The short length of the ammunition means that the portion of the gun inside the mount can be very compact. In the illustration below, the 25mm M242 Bushmaster used in the Mk38 mount is at top right and the Case Telescoped (CT) 40mm is at the bottom right. It’s very compact breech mechanism is apparent.


Image source:

If this gun could replace our 25mm guns on the Webber class WPCs and the Offshore Patrol Cutters, either by replacing the mount or perhaps by replacing the gun in the Mk38 mod2/3 mounts (also a BAE product), it would give us improvements in range, accuracy, impact, and particularly penetration. Rates of fire for the two systems are the same.


The effective range of the Mk38 has been variously reported as 2500 or 3000 yards. This has been a matter of concern to me because when approaching a suspicious vessel that might be being used to make a terrorist attack, I believe a cutter should remain at a distance such that improvised armaments cannot target specific critical equipment on the cutter (like its one gun mount). Improvised armaments might include heavy machine guns, anti-tank guided missiles, or Soviet era anti-aircraft or anti-tank guns of up to 130mm. From my observations and research, in order to preclude targeting critical systems, the cutter should initially approach no closer than 4,000 yards while its boarding party investigates. .

The NavyRecognition post reports a claim of 4,000 meters (4,373 yards) for CTA’s 40mm. While I have not been able to find a claimed max range for the CTA 40mm, the maximum range for the ballistically similar Bofors 40mm/70 is 13,675 yards (12,500 m). The M242 25mm used in the current Mk38 mod2 has a max range of 7,450 yards (6,800 m). Assuming the effective range is proportional to the maximum range, the CTA 40mm should be able to effectively engage from beyond 4000 yards (3,659m).


The image below, from thinkdefence, shows a comparison of effectiveness against armor using armor piercing fin stabilized fin stabilized discarding sabot (APFSDS) rounds. 


To me, greater armor penetration translates into being able to penetrate the hull and go on to wreck a larger diesel engine than the smaller round.

As far as I can tell, while there is an armor piercing fin stabilized discarding sabot (APFSDS) round for the 25mm, the Mk110 57mm has no round comparable to the APFSDS round offered for the CT 40mm, which has a muzzle velocity of 1,640 meters/second or approximately 5,379 feet/second. The 57mm round would explode shortly after penetrating the skin of the ship, likely before it reached the engine.


Because the 40mm round is about twice as big as the 25mm round, its effective radius is considerably larger.

The image below (also from Thinkdefence) shows a fragmentation comparison between a 30mm airburst round (left) and the 40mm GPR-AB (40mm airburst). The lethal area for the airburst nature at 1,500m is 125m2. Apparently there is no airburst projectile for the 25mm because it is considered to small to be effective. 


Is this gun really ready for “primetime?”

Our friend at has done an extensive examination of the development of this weapon.

The gun has been adopted by the British Army for installation on two types of armored vehicles and the French are also planning on using it in one of their armored vehicles.

Apparently the gun is a success and will probably find additional application, including, hopefully, a version of the Mk38.





This is a post I wrote for CIMSEC for their “Distributed Lethality Week,” but their editor thought it would fit better in their “Naval Force Structure Week.” Had I known the topic, I might have spent more time on ASW. 

The Navy has been talking a lot about distributed lethality lately, and “if it floats, it fights.” There is even talk of mounting cruise missiles on Military Sealift Command (MSC) ships, even though it might compromise their primary mission. But so far there has been little or no discussion of extending this initiative to include the Coast Guard. The Navy should consider investing high-end warfighting capability in the Coast Guard to augment existing force structure and provide a force multiplier in times of conflict. A more capable Coast Guard will also be better able to defend the nation from asymmetrical threats.

Why Include the Coast Guard?

A future conflict may not be limited to a single adversary. We may be fighting another world war, against a coalition, perhaps both China and Russia, with possible side shows in Africa, the Near East, South Asia, and/or Latin America. If so, we are going to need numbers. The Navy has quality, but it does not have numbers. Count all the Navy CGs, DDGs, LCSs, PCs and PBs and other patrol boats and it totals a little over a hundred. The Coast Guard currently has over 40 patrol ships over 1,000 tons and over 110 patrol craft. The current modernization program of record will provide at least 33 large cutters, and 58 patrol craft of 353 tons, in addition to 73 patrol boats of 91 tons currently in the fleet, a total of 164 units. Very few of our allies have a fleet of similar size.

Coast Guard 82 foot patrol boats interdicted coastal traffic off South Vietnam. (USCG Photo)

Coast Guard vessels routinely operate with U.S. Navy vessels. The ships have common equipment and their crews share common training. The U.S. Navy has no closer ally. Because of their extremely long range, cutters can operate for extended periods in remote theaters where there are few or even no underway replenishment assets. The Coast Guard also operates in places the USN does not. For example, how often do Navy surface ships go into the Arctic? The Coast Guard operates there routinely. Virtually all the U.S. vessels operating with the Fourth Fleet are Coast Guard. There are also no U.S. Navy surface warships home based north of the Chesapeake Bay in the Atlantic, none between San Diego and Puget Sound in the Pacific, and none in the Gulf of Mexico with the exception of mine warfare ships.

In the initial phase of a conflict, there will be need to round-up all the adversaries’ merchant ships and keep them from doing mischief. Otherwise they might lay mines, scout for or resupply submarines, put agents ashore, or even launch cruise missiles from containers. This is not the kind of work we want DDGs doing. It is exactly the type of work appropriate for Coast Guard cutters. Coast Guard ships enjoy a relatively low profile. Unlike a Carrier Strike Group or Navy SAG, they are less likely to be tracked by an adversary.

If we fight China in ten to twenty years, the conflict will likely open with China enjoying  local superiority in the Western Pacific and perhaps in the Pacific in general. If we fight both China and Russia it may be too close to call.


The National Security Cutter (NSC)

This class of at least nine and possibly ten, 418 foot long, CODAG powered, 28 knot ships, at 4,500 tons full load, are slightly larger than Perry-class frigates. Additionally they have a 12,000 nautical mile cruising range. As built they are already equipped with:

  • Navy certified helicopter facilities and hangar space to support two H-60 helicopters,
  • A 57 mm Mk110 gun,
  • SPQ-9B Fire Control Radar
  • Phalanx 20mm Close in Weapon System (CIWS)
  • SRBOC/ 2 x NULKA countermeasures chaff/rapid decoy launcher,
  • AN/SLQ-32 Electronic Warfare System,
  • EADS 3D TRS-16 AN/SPS-75 Air Search Radar,
  • A combat system that uses Aegis Baseline 9 software,
  • A Sensitive Compartmented Intelligence Facility (SCIF)

In short, they are already equipped with virtually everything needed for a missile armed combatant except the specific missile related equipment. They are in many respects superior to the Littoral Combat Ships. Adding Cooperative Engagement Capability might even allow a Mk41 equipped cutter to effectively launch Standard missiles targeted by a third party.

USCG National Security Cutter BERTHOLF (USCG Photo)
USCG National Security Cutter BERTHOLF (USCG Photo)

The ships were designed to accept 12 Mk56 VLS which launch only the Evolved Sea Sparrow missiles (ESSM). Additionally, the builder, Huntington Ingalls, has shown versions of the class equipped with eight Mk41 VLS (located between the gun and superstructure) plus eight Harpoon, and Mk32 torpedo tubes (located on the stern). Adding missiles to the existing hulls should not be too difficult.

LRASM topside launcher concept. The size and weight are comparable to launchers for Harpoon. (Lockheed Martin photo)

The Mk41 VLS are more flexible in that they can accommodate cruise missiles, rocket boosted antisubmarine torpedoes (ASROC), Standard missiles, or Evolved Sea Sparrow missiles (ESSM). Using the Mk41 VLS would allow a mix of cruise missiles and ESSM with four ESSMs replacing each cruise missile, for example eight cells could contain four cruise missiles and 16 ESSM, since ESSM can be “quad packed” by placing four missiles in each cell. Development of an active homing ESSM is expected to obviate the need for illuminating radars that are required for the semi-active homing missiles. Still, simpler deck mounted launchers might actually offer some advantages, in addition to their lower installation cost, at least in peacetime.

Cutters often visit ports where the population is sensitive to a history of U.S. interference in their internal affairs. In some cases, Coast Guard cutters are welcome, while U.S. Navy ships are not. For this reason, we might want to make it easy for even a casual observer to know that the cutter is not armed with powerful offensive weapons. Deck mounted launchers can provide this assurance, in that it is immediately obvious if missile canisters are, or are not, mounted. The pictures below show potential VLS to be considered.

The relatively small footprint of the Mk56 VLS system (pdf) can be seen here on a Danish Absalon-class command and support ship (beam 64 feet, by comparison the National Security Cutters’ beam is 54 feet). Two sets are visible in the foreground, one set of twelve with missile canisters with red tops in place to the right, on the ship’s centerline, and a second set of twelve without canisters to the left. The Absalon-class has three twelve-missile sets, with the third set off camera to the right. (Royal Danish Navy)
12 earlier Mk48 mod3 VLS for ESSM seen here mounted on the stern of a 450 ton 177 foot Danish StanFlex300 Flyvefisken-class patrol boat. The Mk56 launchers replace the Mk48s with an approximate 20% weight savings.
The Offshore Patrol Cutter (OPC)

The OPC  program of record for provides 25 of these ships. A contract has been awarded to Eastern Shipbuilding Group for detail design and construction of the first ship, with options for eight more. The notional design is 360 feet long, with a beam of 54 feet and a draft of 17 feet. The OPCs will have a sustained speed of 22.5 knots, a range of 10,200 nautical miles (at 14 knots), and an endurance of 60-days. It’s hangar will accommodate one MH-60 or an MH-65 and an Unmanned Air System (UAS).


Notional design characteristics and performance of the OPC. (USCG Image)

It will have a space for a SCIF but it is not expected to be initially installed. As built, it will have a Mk38 stabilized 25 mm gun in lieu of the Phalanx carried by the NSC. Otherwise, the Offshore Patrol Cutter will be equipped similarly to the National Security Cutter. It will likely have the same Lockheed Martin COMBATSS-21 combat management system as the LCS derived frigates. It is likely they could be fitted with cruise missiles and possibly Mk56 VLS for ESSM as well. Additionally these ships will be ice strengthened, allowing the possibility of taking surface launched cruise missiles into the Arctic

The Fast Response Cutter (FRC)

The FRC program of record is to build 58 of these 158 foot, 28 knot, 365 ton vessels. 19 have been delivered and they are being built at a rate of four to six per year. All 58 are now either built, building, contracted, or optioned. They are essentially the same displacement as the Cyclone class PCs albeit a little slower, but with better seakeeping and a longer range. Even these small ships have a range of 2,950 nm. They are armed with Mk 38 mod2 25 mm guns and four .50 caliber M2 machine guns.


The first Sentinel-class Fast Response Cutter (FRC), USCGC Bernard C. Webber. (USCG photo)

They are already better equipped than the Coast Guard 82 foot patrol boats that were used for interdiction of covert coastal traffic during the Vietnam war. If they were to be used to enforce a blockade against larger vessels, they would need weapons that could forcibly stop medium to large vessels.

The Marine Protector Class

There are 73 of these 87 foot, 91 ton, 26 knot patrol boats. Four were funded by the Navy and provide force protectionservices for Submarines transiting on the surface in and out of King Bay, GA and Bangor, WA.

File:US Navy 090818-N-1325N-003 U. S. Coast Guardsmen man the rails as the U.S. Coast Guard Cutter Sea Fox (WPB 87374) is brought to life at Naval Base Kitsap.jpg
Photo: KEYPORT, Wash. (Aug. 18, 2009) U. S. Coast Guardsmen man the rails as the U.S. Coast Guard Cutter Sea Fox (WPB 87374), one of four of this class assigned to Force Protection units. (U.S. Navy photo Ray Narimatsu/Released)

If use of these vessels for force protection were to be expanded to a more hostile environment, they would likely need more than the two .50 caliber M2 machine guns currently carried.  The four currently assigned to force protection units are currently equipped with an additional stabilized remote weapon station.


Cruise Missiles

The U.S. Navy currently has or is considering four different surface launched cruise missiles: Harpoon, Naval Strike Missile (NSM), Long Range Anti-Ship Missile (LRASM), and Tomahawk. Of these, LRASM appears most promising for Coast Guard use. Tomahawk is the largest of the four and both Harpoon and NSM would be workable, but they do not have the range of LRASM. The intelligence and range claimed for the LRASM not only makes it deadlier in wartime, it also means only a couple of these missiles on each of the Coast Guard’s largest cutters would allow  the Coast Guard’s small, but widely distributed force to rapidly and effectively respond to asymmetric threats over virtually the entire U.S. coast as well as compliment the U.S. Navy’s efforts to complicate the calculus of a near-peer adversary abroad

Small Precision Guided Weapons

It is not unlikely that Fast Response Cutters will replace the six 110 foot patrol boats currently based in Bahrain. If cutters are to be placed in an area where they face a swarming threat they will need the same types of weapons carried or planned for Navy combatants to address this threat. These might include the Sea Griffin used on Navy’s Cyclone-class PCs or Longbow Hellfires planned for the LCS.

Additionally, a small number of these missiles on Coast Guard patrol craft would enhance their ability to deal with small, fast, highly maneuverable threats along the U.S. coast and elsewhere

Light Weight Anti-Surface Torpedoes 

If Coast Guard units, particularly smaller ones, were required to forcibly stop potentially hostile merchant ships for the purposes of a blockade, quarantine, embargo, etc. they would need something more that the guns currently installed.

The U.S. does not currently have a light weight anti-surface torpedo capable of targeting a ship’s propellers, but with Elon Musk building a battery factory that will double the worlds current capacity and cars that out accelerate Farraris, building a modern electric small anti-surface torpedo should be easy and relatively inexpensive.

Assuming they have the same attributes of ASW torpedoes, at about 500 pounds these weapons take up relatively little space. Such a torpedo would also allow small Coast Guard units to remain relevant against a variety of threats.


Adding cruise missile to the Coast Guard National Security Cutters and Offshore Patrol Cutters would increase the number of cruise missile-equipped U.S .surface ships by about 40 percent.

Coast Guard Patrol craft (WPCs) and patrol boats (WPBs) significantly outnumber their Navy counterparts. They could significantly increase the capability to deal with interdiction of covert coastal traffic, act as a force multiplier in conventional conflict, and allow larger USN ships to focus on high-end threats provided they are properly equipped to deal with the threats. More effective, longer ranged, and particularly more precise weapons could also improve the Coast Guard’s ability to do it Homeland security mission.

Thanks to OS2 Michael A. Milburn for starting the  conversation that lead to this article.

UAE Transport, Former US High Speed Vessel Swift, Hit by Shore based ASCM

There have been numerous reports (and here) that the former US Navy High Speed Vessel Swift has been attacked and apparently destroyed by a Chinese designed but possibly Iranian built C-802 anti-ship cruise missile (ASCM) while transiting the 25 mile wide Bab-el-Mandeb Strait at the southern end of the Red Sea.

Map of Bab-el-Mandeb.png

Map of the Bab-el-Mandeb by Archer90

The missile was launched by a rebel group in Yemen. This not the first report of their use of anti-ship cruise missiles. They have claimed to have hit ships of the Saudi led coalition before. Plus the American built Israeli Corvette Hanit was hit by a Hezbollah launched C-802 in 2006. If we ever get in a situation like MarketTime again, there is a good possibility that even insurgent groups might have ASCMs.

The C-802 is similar in size and capabilities to the US build Harpoon. There is at least one report that the former Swift deployed Mk36 SRBOC.

Thanks to Peter for bringing this to my attention. 


A photo of the vessel, severely damaged but still afloat here:

They are also saying the damage was done by multiple shoulder launched missile (presumably anti-tank guided missiles) rather than a single ASCM.

Guided 57mm Round Being Developed


Navy Recognition reports that BAE is developing a laser or image recognition guided round for the Mk110 57mm gun that equips the Bertholf Class, National Security Cutter (NSC) and is expected to equip the Offshore Patrol Cutter in addition to the two classes of Littoral Combat Ships.

It is referred to as “Ordnance for Rapid Kill of Attack Craft or ORKA (technical designation: MK295 MOD 1).” Which seems to indicate it is not an anti-aircraft round.

Guided rounds are already available for larger caliber weapons. Guess we will have to wait a while to see if it is actually any cheaper than a guide missile like Griffin or Hellfire. We already know the launcher is not cheaper.

Trade-offs in the 378 FRAM

File:USCGC Sherman WHEC-720 Vietnam War.jpg

Coast Guard photograph, PHC Ken Mather, USCGC Sherman (WHEC-720) in her original configuration with a 5″/38 and dual hedgehogs, April 1969. 

This is hardly a current topic, but it is one I have seen discussed several time, most recently in comments on a post about the new Canadian Arctic/Offshore Patrol Ship (AOPS), e.g. why the Coast Guard used the 76mm Mk75 gun on the 378 FRAMs rather than the 5″/54 Mk45.

It is true that, although about four tons heavier, the early model 5″/54 Mk45 mounts were a drop in replacement for the 5″/38 mounts we had on the 378s. It would have appeared an easy choice, but in order to accommodate the additional weight of the Harpoons and CIWS, perhaps the Coast Guard had no choice but to go with a lighter gun. That gun (and its associated firecontrol system) was certainly seen as a significant improvement over what we had had in essentially all respects including reduced manning and maintenance.

If we look at the weights as built that were removed:

one 5″/38 (20.5 tons) and two hedgehogs (14.4 tons), totalling approximately 35 tons

and compare that to some of the weights added

one 76 mm Mk75 gun (8.2 tons), two Mk141 quad harpoon launchers (11.8 tons total), eight Harpoon (6 tons), and a Mk 15 Phalanx CIWS (6.8 tons).  Total approximately 32.8 tons. Plus more weight for the addition of the hangar. Essentially the difference was a wash.

If instead, we had used the 5″/54 Mk45 mod 0 (24.5 tons) in addition to the harpoons and CIWS, the total weight would have been 16.3 tons higher or 49.1 tons.

There are other weights that might be added in calculating the total weight devoted to armaments, but obviously I don’t think this was an excessive amount, there are too many examples of smaller ships with far more weapons. I previously noted, (“OPC-Design for Wartime, Build for Peacetime”) that as built the little 255s had 140 to 150 tons of weapons.

Even so, an additional 16.3 tons topside (even if that is only about 0.5% of the full load displacement) might have been too much for the 378s. I don’t know. Perhaps a former 378 engineer or DCA could enlighten the discussion.

File:USCGC Mellon WHEC-717.jpgPhoto: Navy photo, USCGC Mellon, with 76mm, Harpoon, and Phalanx CIWS

Another Weapon Option, Brimstone/Sea Spear

Thinkdefense recently reported on the test of a new application of the proven Brimstone missile. (They also have some additional video, and excellent commentary.) Three missiles were launched almost simultaneously against five boats (four stopped and one underway at about 20 knots) simulating a swarm attack. The three missiles each hit a separate target.


The thing that makes this missile so interesting is the range of options it provides the user to ensure that the right target is hit and there is little or no chance of collateral damage. It is equipped with an all weather millimetric radar that will show the shape of the target, and in the latest version semi-laser homing. It can be “fire and forget,” but it can also allow a “man-in-the-loop.” It can be given a laser designation and then continue to independently track the target. It has a terrain avoidance feature allowing it to hit targets on the far side of islands. A kill box can be designated so that it will ignore targets outside the box and self-destruct if it passes through the box without finding a target. Multiple rounds can be fired in a salvo, against one or more targets.

Will the US consider it?:

Clearly this weapon is being marketed to the US, including apparently for use on the Littoral Combat Ship as a competitor to an enhanced Griffin. US Special Forces have already shown an interest in the missile.

Diagram source:

“BRIMSTONE is also being proposed as a surface-to-surface missile for deployment within the SEA SPEAR self-defence system against FIACs (fast inshore attack craft–Chuck) and other small surface threats. With a range of deck-mounted launcher options, from single to six-pack configurations, the system’s very small footprint gives it a high level of deck positioning flexibility making it suitable for small vessels such as FACs as well as much larger vessels such as auxiliary ships.”

When you have to hit a target, have to hit a budget and don’t have time to waste.


It is relatively small, about 107 pounds, less than six feet long, and approximately seven inches in diameter. They claim it is suitable for vessels as small as 15 meters (50 feet).


The nearest similar missile in US service right now is the Hellfire. Brimstone developed out of a program to improve Hellfire, so not surprisingly, Hellfire is very similar in size but has a shorter range. Hellfire has been used on the Combat Boat 90 (a 52 foot boat). It does not have the sophisticated dual mode guidance and collateral damage avoidance features of the Brimstone. Several types have been built. Most are semi-active laser homing, but there is a millimetric radar homing version also, but it does not include the man-in-the-loop feature of the Brimstone. The model that appears most useful in a naval environment is the “N” model. The Thermobaric warhead does sound interesting.

AGM-114N Hellfire II
  • Target: Enclosures, ships, urban targets, air defense units
  • Range: 8,000 m (8,749 yd)
  • Guidance: Semi-active laser homing
  • Warhead: Metal augmented charge (MAC) (Thermobaric)
  • Weight: 48 kg (105 lb)
  • Length: 163 cm (64 in)

What would we use it for?

New weapons like this are beginning to give even very small craft the punch that once came only with something like a 5″ gun, but perhaps more importantly it allows a very precise application of force. That should be very important to the Coast Guard in that their units are most likely to operating in and around the US including densely populated areas.

This may not be a ship killing, or even ship stopping weapon (although it might help), but it might be useful against a different type of difficult target. We might someday need to stop a terrorist or an enemy in wartime employing a fast highly maneuverable craft operating inshore or among a number other vessels where gunfire is likely to cause civilian casualties. This system would be much safer, and more likely to succeed, than using guns, in that circumstance.

Too good to  be true?

With the possibility of being surrounded, pushing one button, and wiping out all your enemies, I was reminded of this sequence from the movie “The Last Starfighter.”

More info here:
Brimstone Advanced Anti-Armour Missile, United Kingdom

Farnborough 2012: MBDA completes Sea Spear live firing

Navy Developing Small Anti-Torpedo Torpedo System, Possible CG Use?

The Navy's experimental Countermeasure Anti-Torpedo launches from the fantail of USS George HW Bush in May. US Navy Photo

The Navy’s experimental Countermeasure Anti-Torpedo launches from the fantail of USS George HW Bush in May. US Navy Photo

In an age where missiles can shoot down ICBMs, the only surprise is that this has not happened sooner.

The US Naval Institute News is reporting that the Navy is developing a small torpedo to intercept Russian/Soviet designed torpedoes that are immune to normal acoustic torpedo countermeasures, because they follow the target’s wake rather than passively homing on the ship’s noise. I would expect it to work against other types of torpedoes as well.

The existence of wake homing torpedoes has been known for decades. Not mentioned in the article, but the Germans were working on these in WWII and the British unsuccessfully attempted to make a wake homer before the first World War.

Initial Operational Capability (IOC) of this hard kill system is expected in 2019 with fleet wide adoption by 2035. What are the implications for the Coast Guard, other than perhaps having the countermeasure on our largest ships?

This anti-torpedo torpedo (ATT) might be adapted to become the “ship stopper” I believe the Coast Guard needs to ensure the ability to stop determined terrorists in control of a medium to large ship. With its relatively small charge it might even be usable in more typical law enforcement situations. The Navy might also find it useful if they are engaged in a blockade operation. I wonder if it might also be useful against swarming small boats.

The ATT is only 6.75 inches in diameter, only slightly more than half the diameter of existing light weight ASW torpedoes. It probably weighs on the order of 100 pounds and the warhead is almost certainly less than 25 pounds, but it would likely suffice to destroy propellers and possibly the rudder of even a large vessel. The fact that it would likely stop a vessel without sinking it, might be seen as an advantage. It is also less likely to create collateral damage, and it would be less dangerous to own ship than the carriage of larger torpedoes. It would have a very small footprint and could be carried on even the smallest cutters.

Slide from a Naval Sea Systems Command presentation on the Surface Ship Torpedo Defense system. NAVSEA Image

Slide from a Naval Sea Systems Command presentation on the Surface Ship Torpedo Defense system. NAVSEA Image

Case for the Five Inch Gun

Currently the largest Coast Guard cutters are being equipped with the Mk 110 (BAE/Bofors 57 mm Mk3) gun mount.  By all reports it is a good defensive weapon, effective against air threats and small fast surface vessels. But is this weapon also the most appropriate for the most likely scenarios?

The Choices: Given that we can only consider weapons supported by the US Navy, there are really only two choices, The Mk 45 5″ and the Mk110 57mm; three if you consider the Mk75 76 mm which seems to be going away.

Mk75 76 mm guns, are mounted on the once large, but now rapidly dwindling  FFG-7 class in addition to 378s and 270s. There are currently roughly 50 systems installed, but that can be expected to rapidly decrease with no new installations planned.  Still, this is based on perhaps the most successful post-WWII naval gun, the Oto-Melara (now Otobreda) 76mm, one that is still being installed on some of the most sophisticated new construction foreign made vessels. There has been some talk from USN sources that they may choose to install the Mk 75 on future LCS, but unless there is a change, it looks likely the 270s will be the last operational US vessels to use the Mk75.

The Mk110 57 mm, is found on the National Security Cutter (NSC) and the Littoral Combat Ship. It is also planned for the Offshore Patrol Cutter, and will be used as a secondary mount on the Zumwalt Class DDG. It is based on the Bofors 57mm Mk3, a competitor to the more successful Oto Melara 76mm. There are currently only about six units operational on US ships now, but if all four classes are completed as planned there will be 94 systems afloat.

The 5″ Mk 45, in its three mods, is the most numerous medium caliber gun in the USN inventory, and until the 155mm Advanced Gun System (AGS) becomes operational on the Zumwalt Class DDGs it is also the largest US naval gun. (Only 6 AGS on three ships are currently planned). There are currently about 106 USN mounts afloat. Numbers have declined somewhat particularly with the decommissioning of the Spruance Class. They are still being installed on new construction and planned Burke Class destroyers, but as DDGs with one mount replace cruisers with two, the number is likely to decrease further to between 80 and 90 mounts.  It is also in service with ten foreign navies. It is the most successful mount of its class in the world.

The Advanced Gun System planned for the Zumwalt Class DDGs is simply too large to consider for use on cutters.

Why do we have guns on our ships at all?

  • We use guns to signal, firing across the bow to tell a vessel to stop.
  • We use guns to intimidate law breakers into complying, making it obvious it is futile to resist.
  • To sink derelict vessels that may be hazards to navigation.
  • To protect ports, waterways, coastal areas, and marine traffic from attack in peacetime (PWCS).
  • To fulfill war time roles.

Self defense isn’t a requirement until it becomes necessary to accomplish one of these tasks.

Signalling or intimidating the typical drug smuggler doesn’t require even a 57mm. A .50 cal is usually adequate, and if not a 25 mm certainly is.

Derelict destruction is now rare, but it apparently was a common requirement at least into the ’30s. While rare, as the Anacapa found out, when it was tasked to sink an abandoned Japanese fishing vessel, it may be more difficult that might be expected. Even so, it is rare, and there are other ways to do this mission, so its not really a consideration in the choice of weapons.

The need for a larger weapon only surfaces for the last two purposes, protection of Ports, Waterways, and Coastal Security (PWCS) and wartime tasking.

Forcibly compelling compliance.

Both PWCS and war time roles are likely to require cutters to be able to board and inspect merchant vessels and the ability to forcibly stop or sink them if they do not comply with instructions, regardless of their size. This requirement is likely to surface across the entire range of possible military conflicts from helping an ally in a counter-insurgency to a wide spread multinational conflict including operations against a great power.

If there is a major conflict, we are going to have to quickly neutralize the adversaries merchant fleet, which might otherwise engage in mining, providing intelligence, dropping off agents, supporting submarines, or even have aboard cruise missiles: http://elpdefensenews.blogspot…

The Coast Guard, and the Revenue Cutter service before it, have always needed a capability to compel compliance. Has our ability kept pace with the increased size of merchant ships?

From the 1920s through the the mid ’80s, when the 378s were FRAMed, the weapon of choice for the larger cutters was a 5″, first the 5″/51 and beginning in World War II the 5″/38. The 5″/51 was developed as secondary armament for battleships and also armed light cruisers, and a small number of destroyers. It was larger than the 4″ guns typically found on destroyers before the 1930s, when the 5/38 was introduced. (Destroyers, of course, did also carry torpedoes as their main armament.) Both the four 240 ft Tampa class (completed 1921-22) and the seven 327 ft Secretary Class (completed 1936-37) were built with two 5″/51s and two 57mm six pounders. The ten 250 ft Lake Class (1928-32) Cutters were built with a 5″/51, a 3″/50, and two 57mm.

240 foot Tampa Class cutter, original armament, 2×5″/51, 2x6pdr

From the reports of submarine successes during WWII, based on numbers of ships and total tonnage sunk, I infer that the average merchant vessels of the period, was about 5,000 tons. 20,000 tons was considered a big ship.

I don’t know what the average size is now, but they have gotten a lot bigger. Anything less than 20,000 tons is considered small and they go up to over 20 times that.

Give that size is a primary factor in ship survivability, today’s merchant ships are likely to be much harder to stop than the ships of the 60 to 90 years ago. Are our ships correspondingly better armed?

The boarding scenario minimizes the relative importance of gun range and sophisticated fire control. If the vessel refuses, combat is likely to commence at short ranges. Modern systems are capable of much greater accuracy at a distance, but even in the ’20s, when ranges were even less than now, because boardings parties were transported by pulling boats, virtually every round would have been a hit. There are at least two ways we can compare hitting power, first we can compare the weight of rounds the systems could have put on target and we can also compare the destructive potential of the individual rounds in terms of muzzle energy.

For reference there are the characteristics I used for calculations.

System              Projectile Weight      Muzzle velocity          Rate of fire
–                             (lbs/KG)             (ft/sec and M/sec)      rounds/minute

5″/51                       50/23                     3150/960                   8.5
5″/38                       55/25                     2500/760                  20
76mm Mk 75           14/6.3                    3030/925                  80
57mm Mk110          5.3/2.4                   3400/1035              220
5″/62 Mk45 mod4  70/31.75                 2650/807.7               20

In terms of potential for putting weight of projectiles on target, there is remarkably little difference if we compare the two 5″/51s that equipped the cutters of the ’20s and ’30s with a single mount of any of the modern systems. (Projectile weight x rate of fire)

  • System                  pounds/minute
  • two 5″/51                     850
  • 5″/38                          1100
  • 76mm Mk 75              1120
  • 57mm Mk 110            1160
  • 5″/62 Mk45 mod4       1400

I’m not sure this is the best metric for the task of disabling or sinking a ship. The projectiles need to reach the vitals of the ship. As ship have gotten bigger, the vitals become more difficult to reach and more damage resistant, which would favor the more powerful weapons.

File:USCGC Duane (WPG-33) off Greenland with SOC 1940.jpg

US Coast Guard Photo: The U.S. Coast Guard cutter USCGC Duane (WPG-33) in Greenland waters, circa 1940

The potential of the individual projectiles to penetrate and cause damage is reflected in the muzzle energy.

System                Projectile Weight     Muzzle velocity       Muzzle energy
–                              (lbs and KG)         (ft/sec and M/sec)     MegaJoules

5″/51                          50/23                     3150/960                     21.2
5″/38                          55/25                     2500/760                     14.4
76mm Mk 75             14/6.3                    3030/925                       5.4
57mm Mk110            5.3/2.4                   3400/1035                     2.6
5″/62 Mk45mod4     70/31.75                 2650/807.7                   20.7

Here the oldest system is remarkable in that of all the systems considered, the 5″/51 had the highest muzzle energy. Only the 5″/62 Mk45 mod 4 is close.

File:USCGC Campbell (WPG-32) at New York Navy Yard 1940.jpg

USCGC Campbell (WPG-32) at the New York Navy Yard, in May 1940. USCG photo

Other Wartime Roles:

I have not been privy to war plans in a very long time, and as they say, plans seldom survive first contact with the enemy, but we have the experience of the past to draw on.

In the 67 years since the end of World War II, I do not believe any cutter has fired at an air target in anger. In fact, I know of no occasion when US Navy surface ships have engaged air targets with medium caliber guns. There have been some occasions when Navy vessels and even cutters have engaged surface targets with guns, but by far the most common use has been Naval Gun Fire Support (NGFS), now referred to by the more generic term Naval Surface Fire Support (NSFS). Cutters did it frequently in Vietnam, firing over 77,000 5″ rounds. The US Navy did it in the Korean War, Vietnam, Operation Praying Mantis (1988), and the First Gulf War. It was done during the Second Gulf War by British and Australian ships. The USN was apparently doing NGFS as recently 2007 in Somalia.

Naval Surface Fire Support (NSFS)

The US Navy has an acknowledged shortfall in NSFS capability. The number of ships capable of performing NSFS has dropped precipitously. For those that remain NSFS is a secondary mission to Ballistic Missile Defense (ABMD), AAW, or ASW. If there is a major conflict, they are likely going to be called upon for other missions that will leave them out of position to do NSFS.

The Zumwalt class destroyer with its 155mm advanced gun system was to have been the primary NSFS platform and there were to have been 32 of them, but the program has been cut back to only three.

If the Offshore Patrol Cutters were equipped with a Mk45 5″ they could provide a increase in US naval  NSFS capability out of all proportion to the small marginal increase in cost.

More about the Mk45 5″

File:US Navy 070111-N-4515N-509 Guided missile destroyer USS Forest Sherman (DDG 98) test fires its five-inch gun on the bow of the ship during training.jpg

Photo: US Navy photo by Joshua Adam Nuzzo. USS Forrest Sherman (DDG 98) fires its five-inch gun.

The Mk 45 was originally designed as a direct replacement for the 5″/38 single mount. Destroyers the size of the OPC carried five 5′/38 mounts in addition to torpedoes and numerous 40 and 20 mm guns. Even in its latest version, the Mod 4, its 33 ton weight is not unreasonable for a ship the size of the OPC.

As the most numerous US naval gun a large variety of projectiles are available and there remains great potential for further development. The 5″ is effective against air targets, and special projectiles have been developed for dealing with small high speed surface targets. Add on GPS guidance can make them precision strike weapons in the NGFS role.


In choosing the Mk110 57mm because it was seen as a better AAW weapon, a better anti-swarm weapon, as lighter, cheaper, easier to maintain or man, for whatever reason, the Coast Guard will have a weapon that is at best only marginally more capable, perhaps even less capable, of performing the most likely missions–stopping/sinking a surface target or performing NSFS–than the weapons of 60 to 90 years ago.

While the size, toughness, and survivability of merchant ships has increased dramatically, the Coast Guard has not provided its ships with a significantly improved capability to stop or sink a ship since the introduction of the 5″/51 in 1921. I still think the Coast Guard should add a light weight anti-surface vessel torpedo to its inventory as the cheapest way to have a truly effective ship stopper that can be made widely available. But until such a weapon becomes available, the Mk45 5″ is the best alternative available.

The 5″ Mk45 is a versatile weapon. Equipping the OPCs with this weapon make the ships more capable of performing both the PWCS and probable wartime mission and significantly enhances the NSFS capability of US Naval forces in a major conflict.

File:USCGC Cook Inlet (WHEC-384).jpg

USCGC Cook Inlet (WHEC-384), USCG photo

File:USCGC Duane (WHEC-33) returning from Vietnam 1968.jpg

USCGC Duane (WHEC-33) steaming home after completing her tour of duty in Vietnam, 1968. USCG photo

File:USCGC Rush WHEC-723.jpg
Photo: USCGC RUSH (WHEC-723) underway during Exercise Brim Frost ’85. photographer: SGT. Zachs

A photo of the Half Moon firing her main battery.

5″/38 fired from a Coast Guard 311 ft WHEC

New Gun Coming to a Cutter Near You?

Defensemedianetwork is reporting BAE is showing a new generation of the Mk38 gun mount that already equips several Cutters. In additions to improvements to the system as a weapon, there are also improvements to the associated electro-optic system that should make it even more useful for SAR, LE, and navigation.

Mk 38 30 mmThe mount is enclosed. The gun caliber increases from 25mm to 30mm providing more range and there is a coaxial .50 caliber. Maximum elevation of the mount is increased from 40 to 75 degrees. Ready ammunition on the mount is tripled.The display and control system is improved and there is a mode specifically designed for firing warning shots.

Photo: Mk 38′s 30 mm cannon with coaxial machine gun. The stealth faceting of the mount is obvious in this shot. Photo by Mrityunjoy Mazumdar

(Thanks to Lee for pointing this out)