The Mk38 and Ballistics and Weapons Effectiveness Lessons from Pursuit of the Graf Spee, Part 2

Part one recounted an engagement in 1939 between the “pocket battleship” (heavy cruiser) Admiral Graf Spee and three smaller British cruisers. This part will discuss the implications.

So what does a 77 year old Naval battle have to do with the Coast Guard’s ability to stop a terrorist attack using a medium to large ship?

As I said in part one (in a different order), I think it shows:

  • It is very difficult to sink a ship by gunfire alone.
  • Ships’ structure provide a degree of protection that makes it difficult to comprehensively target the crew of a ship without sinking the ship.
  • It is difficult to forcibly stop a ship with gunfire alone.
  • In comparing guns, at any given range, the longer ranged weapon generally enjoys an advantage in accuracy.
  • You can run out of ammunition before you accomplish your mission. The depth of your magazine may be important.

What do we have to oppose this type of attack?:

We don’t really have a lot of options.

If we have enough warning, say 24 hours, we can ask for help, but as far as I can tell there is no system of rapid response to surface threats. (When 9/11 occurred, we had no system for rapid response to air threat.) Unless we have absolute proof that the vessel in question is hostile, the Coast Guard would almost certainly have to intercept the vessel to determine hostile intent before it could be attacked. If the threat is a 20 knot ship detected 200 miles from its target we will have only ten hours to deal with the threat, and we are likely to be considerably less.

We have one Maritime Security Response Team (MSRT) on each coast, but to mobilize them, brief, organize, transport, and then get them to where we want them to act may take considerable time. Additionally while they might be effective in retaking a hijacked merchant ship, where there are relatively few hostiles who also have to control the crew, attempting an opposed boarding of a ship crewed by armed terrorist as a first step toward stopping an attack may be suicidal. If we have time to get them into place then perhaps we would also have time to get help from other services.

I think it more likely we will have at best a few hours to deal with the threat and we will have to use forces already in the area. I’ve made suggestions about additional equipment we might use to address this threat (here and here), but this time I will discuss tactics using what we have, or plan to have, and limit equipment suggestions to minimal upgrades and choice of ammunition.

While I doubt we will have cutters armed with 57mm Mk110s or 76mm Mk75s, on scene when required, we will discuss their utility and limitations. The Mk38 seems to be the key system, widely available and potentially capable, if the right ammunition is available. Other systems, .50 caliber and smaller, appear ineffective in stopping medium to large ships, but they may have their uses.

It is very difficult to sink a ship by gunfire alone:

Each of the Graf Spee’s 11.1″ projectile weighed 125 times the weight of a 57mm shell or roughly the weight of all the projectiles in a 57mm Mk110 gun mount’s 120 round automatic feed system.

Graf Spee was hit 20 times, three times by 8″ and 17 times by 6″ for a total of 2,672 pounds of projectiles. That is roughly the equivalent of being hit 500 times by a 57mm. From a distance, other than the burned out scout plane she carried, it would have been difficult to tell that she had been hurt.

Exeter was hit at least seven times excluding damaging near misses. That was 4,627 pounds of projectiles, a weight, I believe, almost equal to the total weight of all the 57mm projectiles allowed on a National Security Cutter (about 5,300 pounds assuming 1,000 rounds). While heavily damaged, Exeter was still capable of making 18 knots and completing the approximately 1,000 nautical mile journey to the Falklands.

Neither of these ships would be considered large by current standards. We can conclude, we are unlikely to sink a medium to large merchant ship with any weapon in the Coast Guard inventory.

Ships’ structure can provide a degree of protection that makes it difficult to comprehensively target the crew of a ship without sinking the ship.

Personnel Casualties were relatively light. Out of the approximately 3,000 men on the four ships, there were only 108 killed and 88 wounded.

  • Commonwealth: 72 dead (Achilles 4, Ajax 7, Exeter 61), 28 wounded
  • Germans: 36 dead, 60 wounded

As severely damaged as Exeter was, less than one in ten of the crew was killed. Unless terrorists choose to expose themselves, gunfire, from either cutters or airborne use of force equipped helicopters, is unlikely to allow us kill enough terrorists to stop an attempt to use a medium or large ship to make an attack.

Can We Immobilize the Target?: 

None of the four ships were immobilized.

Of the approximately 30 hits, only one hit a main machinery space and it appears this was not because armor kept rounds out. It was simply that the amount of machinery space above the water line is a very small percentage of the total exposed area.

The single projectile that entered a machinery space was an armor-piercing 8″ round, and it wrecked the Graf Spee’s fuel oil purifier.  That made it virtually impossible for the ship to make it back to Germany without having work done in port over an extended period. That would have allowed Britain to guarantee that Graf Spee would never escape, but it did not stop her from transiting at full speed for about 14 hours.

A modern merchant vessel diesel engine. 

The task of stopping a ship by gunfire actually may have become more difficult because of the size and toughness of modern large diesel power plants, and because the large size of modern vessels puts more of the engine below the waterline and provides more space between the ships sides and the propulsion machinery.

The ship featured in the video above is no longer particularly large. The new Panama Canal locks needed to be wider and deeper than the old ones to accommodate the larger ships that have now become common. The locks are now 180 feet (vs 110 feet) wide and 60 feet (vs. 42 feet) deep. Many ships now have sufficient draft such that the 40 foot tall engine in video could be entirely below the water line.

Fuel consumption for the engine in the video above was reported twice, first as 328 tons per day and later as 400 tons per day. If we assume only 300 tons per day, that is 12.5 tons per hour or 417 pounds /minute or about 7 pounds per second.

The explosions going off in this type of engine every second are more powerful than the explosion of a 57mm shell. 

There is less than a pound of explosive in a 57mm projectile. 1 pound of TNT has 13.4 megajoules of energy. We may assume a more powerful explosive in the Mk110 projectiles, perhaps 20 megajoules. One gallon (about 7.1 pounds) of diesel (the amount consumed in one second) equals 146.5 megajoules.

The 57mm gun does not have a true armor-piercing round. The current 3P fuse has a semi-armor piercing function which I presume is similar to the previous semi-armor piercing (SAP) round, “The SAP round had a delayed action fuze which allowed the round to penetrate about 2 cm (0.8 inches) of armor and then explode after traveling a further 2 m (6 feet).” If that is the case, first it is uncertain that the round will penetrate, since the plating on large ships can considerably exceed 2 cm, but assuming it did, an explosion two meters inside the hull would still be a long way from a very tough engine.

The 76mm Mk75 is the most powerful gun in the Coast Guard inventory, but we have fewer of them every year, although it looks like we will not see the last of those on the 270s until 2034. It is still a relatively small projectile at about 14 pounds. Like the 57mm there is no true armor-piercing round for this weapon. Like the 57mm its projectile would likely explode shortly after penetrating the hull, rather than on or in the engine. The 57 and 76 mm guns might have more success against the steering gear, but that will also be very robustly built on any large ship, and hitting it will require great accuracy, suggesting a close approach.

The Mk38 25 mm, with a maximum shell weight of 1.1 pound or less, might be assumed to be even less likely to do damage, but they do have an option for an armor-piercing fin stabilized discarding sabot round (APFSDS) (pdf). It is intended for use against lightly armored vehicles like Armored Personnel Carriers. It may not be commonly available for the Mk38 (the Navy thinks of the Mk38 exclusively as a counter to small craft), but the APFSDS round is in the Navy system for use by Marine LAV-25 Light Armored Vehicle. It fires a 98 gram (3.5 oz) Solid Tungsten Penetrator at a very high velocity, 1390 m/sec (4560 ft/sec).

25MM TUNGSTEN APFSDS-T Armor Piercing Fin Stabilized Discarding Sabot-Trace

Armor Piercing Fin Stabilized Discarding Sabot-Trace

The .50 caliber, 7.62 and 5.56 mm weapons are simply too light to make much impression on a medium or large ship. The only other CG gun with a possibility of forcibly stopping one of these vessels is the Phalanx 20mm Close In Weapons System (CIWS). This system uses a discarding sabot round 12.7mm in diameter Solid Tungsten Penetrator with a 3,650 fps (1,113 mps) muzzle velocity. The Phalanx is only found only on WHECs and NSCs, so they will soon be home ported only in Charleston, Alameda, and Honolulu and it is unlikely these ships will be available to respond.

If we do detect a terrorist attack, the only likely Coast Guard counter to it, is likely to be equipped with a Mk38 mount. We are not going to sink a medium or large ship with the Mk38, but we might be able to disable it, if we can accurately penetrate both the ship’s hull and the ship’s engines or disable the steering.

In comparing guns, at any given range, the longer ranged weapon generally enjoys an advantage in accuracy.

I started thinking about the results of the Battle of River Plate after reading this pdf, Offshore Patrol Cutter (OPC) SUW Self-Protection Secondary Battery Study (which compared one and two-gun solutions using .50 cal., 25mm, and 30mm) and writing a post about a possible 40mm alternative for the Mk38 gun mount currently used on the Webber class WPCs and planned for the Offshore Patrol Cutter. It occurred to me that everyone may not understand my strong preference, when considering guns, for the longest ranged weapon available, even if I don’t expect it to be used at extreme ranges.

It is not just the potential of longer range, or the fact that the projectile is probably larger and more effective. It is also the fact that, all other factors being equal, the longer ranged weapon is also almost always more accurate.

Comparing any two weapons, fired at a target at the same range, the longer range weapon will generally fly a flatter trajectory (a more direct path) and have a shorter time of flight, meaning it will be effected less by uncertainties of environment and the actions of the target between firing and impact.

In the battle we see three gun with different ranges and can compare their accuracy. If we look at the British 6″ guns as a base line, how did the weapons compare?

The British 6″ gun had a maximum range of  24,500 yards (22,400 m). They got hits 0.82% of the time.

The British 8″ gun had a maximum range of 30,650 yards (28,030 m), 25% greater range, got hits 1.55% of the time, making them 89% more accurate than the contemporary 6″ guns.

The German 11.1″ had a maximum range of 39,890 yards (36,475 m), with 63% greater range than the 6″ guns, got hits 2.4% of the time, making them almost three times as accurate as the 6″ guns at the ranges the battle was fought (193% more accurate).

While it might be argued that the Graf Spee benefitted from superior fire control, the same cannot be said for the Exeter’s 8″ guns, that for most of the engagement were fired under local control. Additionally it appears that the light cruisers’ director controls were at least as sophisticated as that on Exeter. It appears the greater accuracy is due to the flatter trajectory and shorter time of flight of the longer ranged guns.

40 mm case telescoped gun (bottom) compared to conventional guns.

40 mm case telescoped gun (bottom) compared to conventional guns.

There are at least four different gun calibers that can be mounted on the Mk38 gun mount, 25, 30, 35, and 40mm. If we have the opportunity to upgrade the Mk38s to higher caliber weapons, we should take it, not just for the greater effectiveness of the projectile but also for the likely greater accuracy and effective range.

Case Telescoped 40 mm ammunition

Case Telescoped 40 mm ammunition

Making the Best of the Mk38

“No captain can do very wrong if he places his ship alongside that of the enemy.”–Horatio Nelson

When I looked at this problem earlier, I suggested that we should have systems that could disable a ship at ranges greater than 4,000 yards, so that weapons on the terrorist controlled vessel could not target specific systems on the defending cutter. With what we have now, we don’t really have that option. We are going to need to get a lot closer.

Not only is the effective range of the Mk38 less than 4,000 yards, we will need to get closer to increase accuracy to target specific parts of the terrorist vessel, and close the range to maximize the kinetic energy of the rounds.

If we are to have any chance of stopping a medium to large ship making a terrorist attack, we need to do what the British did. We need a team approach. We need to gang up on it.

The only ships we have that might have a chance are those with 25mm and larger weapons. There are relatively few of those. They would be the primary shooters. Hopefully you would have more than one to respond, but in many cases, perhaps most, there would be only one.

We can still use less capable units to take pressure off the primary shooter. These supporting units equipped only with .50 caliber and smaller weapons might be used to target the bridge, but their primary function should be to target any weapons that might endanger the more capable cutter(s). 

Targeting the bridge is relatively simple, but if the terrorists plan properly they will not need to navigate from the bridge. They can use an autopilot or steer from after steering.

As we approach we will want to establish hostile intent as early as possible, preferably without putting a boarding party aboard that might become hostages.

We can demand that the vessel stop or change course away from the endangered potential target. The quickest way to do that might be with an Airborne Use of Force helicopter. Other supporting units might also be sent ahead of the primary shooter to attempt to stop or turn the suspect vessel.

After establishing hostile intent, supporting units should, if possible, precede the primary shooter and engage the threat with the idea of suppressing any weapons the vessel might employ against the cutters.

As it approached its target, before attempting to disable it, the primary shooter should probably put a few rounds into the bow of the target, in case it has been loaded with explosives.

Because the supporting units will need to stay out of the line of fire between the primary shooter and terrorists’ vessel, and because projectile will lose the minimum amount of kinetic energy if it strike normal to the target’s side, the primary shooter should move to a position on beam of the threatening vessel, while supporting units should be both forward and aft of the primary shooter’s line of fire, ready to engage any attempt to return fire.

If the supporting units include a unit with only one machine gun on the bow, like a Response Boat, Medium (RB-M) and a unit with machine guns both fore and aft, like an 87 foot WPB, the WPB should be positioned toward the bow of the target, so that it can parallel the target and still have weapons on target while the unit (RB-M) with only gun on the bow, can keep its weapon on target.

An airborne use of force helicopter could also be very useful as a supporting unit, taking out any terrorist who appeared on deck and keeping an eye out for their activities on the disengaged side of the vessel.

At some point the primary shooter is going to have to close alongside, so that it can shoot through the hull near the waterline, down and into the engine room below the waterline. The supporting units should get there first, shoot up the bridge, attempt to draw fire and suppress any return fire.

When the primary shooter comes alongside ready to attempt to disable the terrorist vessel it will need a lot of ammunition so it will need to exercise fire discipline during the approach.

If we are unable to disable the engine(s) or steering, as a last ditch effort, we can attempt to push the vessel into shoal water and run it aground. This would of course make the cutters easy targets for grenades and RPGs.


The approach outlined above implies a desperate fight, with no guarantee of success. If the terrorists manage to knock out the few (or one) weapon capable of stopping them, we might have no chance of success.

This is not the kind of fight the Coast Guard should want. It puts our people, our mission, and the people we are supposed to protect in danger. Right now there is no assurance that 25mm can even do the job.

We really ought to do better.

The Future:

I would hope the Coast Guard would do some testing to find out if we have the weapons we need to stop the full range of possible maritime terrorist attacks.

That should help us pick the right ammunition. We really need to make sure we have the right types. of ammunition. 

If tests show we cannot disable the largest ships, we need to insist that we get weapons that can, and they may not be standard US Navy weapons.

Alternately, we need to establish means to have other services deploy anti-ship weapons on short notice. (Coast Defense is still officially an Army mission.)

We noted earlier that a new Mk38 mod3 mount is on the way.  It will have much more ammunition on the mount. While the mount appears designed for a 30mm gun, it appears we will be getting them equipped with 25mm guns. More ammunition is good, but a larger weapon would be better.

Guns may not be the answer, but any upgrade we can get in the caliber of the gun on the mount will permit it to be more effective against progressively larger ships and at longer range.

In the not too distant future we will need to start replacing the 87 foot Marine Protector class WPBs. The oldest are already 18 years old. As soon as the last Webber class is funded, we need to start funding 87 footer preplacements. Hopefully we will see fit to arm these vessels for this mission.

30 thoughts on “The Mk38 and Ballistics and Weapons Effectiveness Lessons from Pursuit of the Graf Spee, Part 2

  1. Fascinating set of posts. Does it affect your analysis that, unlike a WWII warship, a hijacked merchant ship is not heavily armored and compartmentalized? Nor do they have substantial heavy weapons of their own, meaning that an attacking Coast Guard ship could get within 500-1000 yards to fire. That would likely create a hit percentage much much higher than of the Graf Spee or the British ships.

    • Actually merchant ships, particularly tankers can be very tough. They have many compartments

      If you take a look at the results of attacks on merchant ships during the “Tanker War” you will see a lot of attack, including many by Iraqi Exocets, but relatively few sinkings.

      As far as their weapons, they need not be limited to AK-47s and RPGs. In additiion to heavy machine guns, they might use highly portable anti-tank missiles, shoulder fired anti-aircraft missiles, even Soviet era anti-tank and anti-aircraft guns that range up to 130 mm. That is why I would prefer to have a capability with high probablity of success at a range of at least 4,000 yards.

      Because we do not have that capability, in this scenario I suggested that we would need to aggressively neutralize any attempt at return fire from the terrorist vessel.

      • Merchant ships are tough, but nowhere near as tough as armored warships. The Graf Spee’s main armor belt was ~3 inches thick. And I seriously doubt that even compartmentalized merchant ships will either be fully locked down (ie have all the watertight hatches closed) or will actually be effectively watertight (a lot of warships turned out to be much less watertight than thought because of breaches in the protection for cable runs, etc). I think you need to account for that in your analysis.

        Nor, I note, does the terrorist merchant ship need to be sunk; it needs to be stopped. Just like with the Bismarck, targeting the steering and propulsion is a much quicker kill than sinking the ship.

        Finally, on range, you had already moved in from 4,000 yards in your last post:

        “When I looked at this problem earlier, I suggested that we should have systems that could disable a ship at ranges greater than 4,000 yards, so that weapons on the terrorist controlled vessel could not target specific systems on the defending cutter. With what we have now, we don’t really have that option. We are going to need to get a lot closer.”

        In terms of defensive weapons, we could just as easily speculate that the terrorists might have Exocets, which makes 4,000 yards just as dangerous. At some point, you have to decide on what’s within the range of plausibility, and I think that tops out at RPGs (and *maybe* ATGMs).

      • @Total900, The point of the tactic was in fact to try to stop the ship and I specifically talked about targeting propulsion and steering. That would hopefully give us time to bring in the heavy hitters from our sister services.

        I noted I would like for the Coast Guard to have a weapon effective outside 4,000 yards (specifically because of ATGMs), but with what we have, we have to get closer.

        Warships are ton for ton tougher than merchant ships, but on the other hand,they don’t have to be. We are not shooting 8″ either.

        A major component of survivability is size and todays merchant ships are huge. Also unlike WWII warships they do not have huge amounts of ammunition that may result in magazine explosions an av gas for aircraft that lead to fires.

        During the Tanker wars, FFGs that were escorting tankers would follow the tankers because if a tanker hit a mine it was no big deal. If the FFG hit a mine, it was in big trouble.

      • Overall, I have to agree with total900 here. Warships (especially the ones being discussed) have armor, they have compartmentation and two other factors not yet discussed:

        Warships’ layout is optimized for mission first, survivability second, and everything else a far, far distant third, while merchants are laid out for low-cost/mission-accomplishment (which never has to do with survivability or being shot at) tied for first, efficiency second, seaworthiness/following shipping regulations tied for third, and everything else fourth… It is very hard to quantify how this plays into Chuck’s analysis (or conclusions I guess might be better), but it is easy for even a lay person to see the differences are drastic.

        Second, warships have EXTREMELY large crews compared to merchantmen, and a significant portion of the crew is committed to damage control. The personnel in the DC parties on Exeter probably outnumber the entire crew of a tanker or container ship. This “active defense” of a warship’s survivability can and should not be underestimated when comparing and drawing conclusions about ship’s seaworthiness and survivability in the scenarios you’re bringing to the fore, Chuck.

  2. I would expect that in any of these situations an F-18 or F-15 could be there within minutes with a suitable missile and convert one ship into two ships. The U.S.C.G. does not stand alone.

    • You might assume that, but as far as I can tell, there are no pilots trained in anti-ship procedures sitting in attack aircraft, armed with appropriate weapons waiting for the call on strip alert.

      We barely have an AAW alert force and only because of 9/11.

      It takes hours for the mission to be approved, crews called and briefed, planes readied, fueled, and armed, and the aircraft to transit to the area they are needed.

      Then we have the issue of the air crews recognizing the correct target. This is why I have suggested that all CG cutters shoul have a laser designator available.

    • I agree with Chuck, emphatically. Prior to 09/11, The USAF had upgraded the capability of some B-52s to carry and launch Harpoon. Other than that, the extent of the USAF in anti-shipping operations would probably be AGM-65 Mavericks.

      Most USAF planes, like the F-16 were designed/equipped to carry and launch Harpoon, but how many Harpoons are in the USAF inventory? Given the 5-10hr window of warning (if we’re lucky), how many Harpoons are close enough from USN weapons stations to be trucked to a nearby USAF base? And even then, who is trained and qualified to install and wire them? And this is assuming the planes retain the Harpoon capability designed into them 30+ years ago after innumerable avionics upgrades? And how many USAF pilots are up-to-date qualified on the Harpoon?

      It’s much more plausible AGM-65s would be usable, and an E/O seeker would be ideal for targeting the bridge, but that’s the best to be hoped for, and that is still a long stretch. Why? Because the USAF post-09/11 CONUS defense mission has focused on air threats. F-15s and F-16s sit with Sparrows and Sidewinders afixed to take out an airborne threat, but no Mavericks are hanging from the wings… Still, given there are Mavericks on the base (something I doubt heavily), it is possible, they could be installed on short notice. And, pilots and ground crew would be experienced in handling and operating that system. Still, with a non-armor-piercing 500-lb warhead, they aren’t going to “blow a (large merchant) ship in two.” But they would be sufficient for a mobility kill.

      • Most bombs and shells will explode on contact. In most cases if the target is a merchant ship, that is a long way from the engineroom. Unless we not only get into the engineroom but also get directly at the engine, we are unlikely to hurt it.

      • @ Lyle: True, I suppose the USN P-3/P-8 Patrol squadrons regularly operate with ordnance from CONUS and are usually available.

  3. I really enjoyed reading this analysis, but I think the conclusions have gone astray. Chuck, you’ve spent a lot of electronic ink laying out how hard it is to sink a ship. As evidence, you’ve pointed out that Graf Spee’s 11″ and the British 6″ and 8″ guns were insufficient to sink their adversaries. Finally, you’ve made a strong argument that, due to several factors, large merchantmen might be almost as hard to sink as those WWII warships. (You may not have said that outright, and you may not have even meant that, but it is certainly a strong impression given off by the post.)

    First, I think the replies above in total900’s discussion have already dealt with the toughness of merchantmen vs. a warship.

    However, then we come to the conclusions about gunfire. I think you’d have been better off analyzing the Battle of Samar.

    A snippet from wikipedia (because I’m getting lazy… 🙂 —
    “Gambier Bay was fired on and hit by multiple Japanese ships. At about 0820, Gambier Bay was severely damaged by an 8 in (200 mm) shell from the Japanese Heavy Cruiser Chikuma which flooded her forward engine room, cutting her speed in half.[1] Gambier Bay was soon dead in the water as the battleship Yamato closed to point blank range. Yamato is clearly seen in the background of photographs taken during the attack on Taffy 3.[2] Fires raged through the riddled escort carrier, and she capsized at 0907 and sank at 0911.”

    Note that Gambier Bay was hit numerous times by numerous ships, including possibly the 18″ guns of the Yamato. However, it was a single 8″ shell which cut her speed in half by flooding her forward engine room. Three things to note:

    1) She had separated engine rooms, something most merchantmen do not have today.

    2) The single 8″ shell had it’s effect by “flooding the engine room.”. It has been reported the Japanese thought they had encountered much larger warships and were loading and firing armor piercing in their large-caliber guns. The effect this had on the unarmored escort carriers and DEs was that the shells completely penetrated without going off. Thus, the effectiveness of that one 8″ shell was not in its explosive force, but in the fact that it opened an 8″ hole to the sea which was un-patchable.

    3) That single 8″ shell, had the Gambier Bay had only one engine room, would have been a 100% effective mobility kill, as we are looking for, regardless of what other Japanese ships fired upon her.

    Point number two brings up another factor you haven’t considered in looking at the Battle of the River Platte, or considering WWII or other examples of large-caliber naval gunfire. You did not take into consideration the effect of plunging fire. Most naval guns have sought more velocity to increase accuracy and range. One must remember that each caliber has its own trajectory, and in about the last 1/3 to 1/4 of that trajectory, the projectile is falling at a fairly steep angle. Thus, during the Battle of the River Platte, by the time the ships were close enough together for the British 6″ shells to strike Graf Spee, the Graf Spee’s 11″ guns were firing very horizontally in the flat first 2/3s of their trajectory. This caused those 11″ shells to hit the cruiser’s armor where it was thickest and virtually eliminated creating any 11″ holes below the waterline on the British ships, which would have been devastating.

    Back to the Gambier Bay. The Casablanca-class benefitted from being designed as escort carriers from the keel up. Thus, the benefit of having two, separated engine compartments. However, they were still built no heavier than a merchantmen, having no armor, other than some splinter plating around control stations and the hangar torpedo stowage area, with no underwater protection whatsoever. Henry Kaiser managed to build these CVEs in 3 months on average… At 500′ and 11,000 tons, the Gambier Bay would be a little small compared to an LNG tanker or containership today, but her layout and separate engine rooms made her somewhat robust for her size.

    The conclusion from the Battle of Samar, specifically the Gambier Bay sinking, is still consistent with your point, though not so drastic. With the threat we’re discussing, the key seems to be penetration, not explosive effect. The penetration needs to penetrate the hull at or below the water line, and must create enough flooding to disable the engine space. Practically speaking, we’re really talking about a torpedo, as Chuck has brought up many, many times. Otherwise, we need to go back to 5″ guns and AP shells on all the OPCs and NSCs (something which will not happen).

    • And, changing from 25mm to 40mm will accomplish nothing. In fact, going to the Mk.110 57mm or the 76mm will not be effective. Even in your past post about the difficulty in sinking an undefended warship with no DC parties and whose water-tight protections are not perfect in a sinkEX, it is clear large guns and even missiles will at best create a mobility kill, as hits must engage the waterline or deeper through the hull to effectively sink a ship with any speed.

      Frankly, given the assets available, this is probably why the MSRTs were stood up. They are the most definite way to stop the threat. The problem is the low number of them and how spread out they are. Every MSST would need some upgraded training and there would need to be trained aviation assets available to give coverage to all of the high-value port areas in CONUS.

      • Yes I see no prospect of being able to sink a ship with what we have, the best we can hope for is a mobility kill, but for our purposes a mobility kill is probably enough.

        Doing a opposed boarding really against a ship crewed by armed terrorists with a death wish seem suicidal, at least if there isn’t a lot of suppressive fire done before the attempt, a good way to loose not only the boarding party, but also the helicopter or boat that deliviers them.

    • Gambier Bay was only one of two US Navy ships of more than 3500 tons full load (destroyer size) that were sunk by gunfire alone, and in both cases gun of 8” or larger were involved. The Japanese had a fixation on the idea of shells falling short, passing through the water and striking the target’s hull below the armor belt. For this reason they had extra long delays on their fuses. It appears that Gambier Bay was one of the few occasions where the projectile actually penetrated the hull below the water line.

    • In response to this,

      ” Thus, during the Battle of the River Platte, by the time the ships were close enough together for the British 6″ shells to strike Graf Spee, the Graf Spee’s 11″ guns were firing very horizontally in the flat first 2/3s of their trajectory. This caused those 11″ shells to hit the cruiser’s armor where it was thickest and virtually eliminated creating any 11″ holes below the waterline on the British ships, which would have been devastating.”

      I suspect you are talking about the possibility of projectiles landing short and penetrating the hull below the armor belt, because penetrating the armor belt, which protects the waterline, gets easier as the range closes.

      Penetrating deck armor does get easier as the range increases, because the projectile strikes the deck nearer to normal (vertical). On the other hand side armor which is essentially vertical gets easier to penetrate as the range closes, since the flatter the trajectory the closer to striking normal to a vertical surface and of course the more energy the projectile retains.

      • Yes, exactly, but the conclusion to draw is that, at close range, where the guns’ trajectory is flat, the destructive force is going to be against men and machinery above the waterline. Thus, the difficulty in sinking via gunfire. (And, I postulate, a mobility kill is probably just as unlikely, if the engines are buried in the hull below the waterline as you describe.)

        Most ships sunk in warfare are sunk by three mechanisms: torpedo (either against the side or beneath the keel, but either way, disrupting watertight integrity), Aerial bombs (falling from above, have the same effect as plunging gunfire (disrupting watertight integrity at or below the waterline), and plunging gunfire (again, disrupting watertight integrity at or below the waterline). (This is also why many modern anti-ship missiles perform a “pop-up maneuver,” at the end; it’s not just to avoid countermeasures…)

        When talking about the 25mm, 40mm, 57mm, and 76mm, these are all poor penetrators. Heavier projectiles penetrate better. (Materials and design can make up for this a bit, usually giving the performance of about one caliber larger, but velocity and weight do not change meaningfully.).

        The other benefit of the heavier gun is often they will be lower velocity, allowing plunging fire which the small-caliber/high-velocity types do not. Imagine the early-/pre-WWII 5″/25-cal and it’s low velocity. The projectiles could practically be seen flying in their rainbow trajectories to fairly short range. But, when it fell, it was still a 100-lb projectile, thus hitting with good force. Now imagine the 25mm. It’s benefit is high velocity, theoretically making hits easier. Still, we need plunging fire. To a large merchantman, a plunging 25mm is going to feel like fleas to a dog: annoying, but not mission-stopping.

  4. And, to bring back some other points in prior discussions we’ve had:

    A practical alternative to sea-borne assets would be a shore-based Harpoon launcher combined with a drone system which could loiter, track, and designate the Harpoon onto the target vessel (something extremely necessary in busy shipping lanes in the port approaches). By avoiding the use of sea-borne assets and traditional aviation assets, these systems, under the control and operation of the local Sector Ops Center, would be FAR less likely to be out-of-position or tasked with other missions when needed for these crises.

  5. @Bill Smith, I’ll try to address some of your comments here.

    The purpose of the was to suggest what we can do with the systems we have now.

    I think it is clear we do not have any systems now, that would allow us to reliably open the hull of any substantial merchant ship sufficiently to cause it to sink or even flood the engineroom expeditiously. Consequently we need to disable either the engine or the steering.

    There seems to be an assumption that that if we penetrate the hull and there is an explosion, we will have accomplished that. I don’t this is case unless we are very lucky. Most of the engine and steering components are very robust, becoming increasing more so as the size of the ship increases.

    To do any damage with what we, have the cutters are going to have to get very close and to allow them to do that will likely require suppressive fire to prevent damage to the cutter and its critical systems. I also doubt that we currently have the APFSDS ammunition we would need to damage one of these monster engines.

    If we want to talk about bringing in other systems or other services, that is a different discussion. I see four possibilities:

    1. Put light weight anti-ship torpedoes on the CG patrol boats that are the most likely asset to be on scene when needed.
    2. Put LRASM or comparable Anti-Ship Cruise Missiles on all large cutters.
    3. Get commitments from other service to have crews and aircraft armed and ready to respond if the threat develops.
    4. Create a new organization on shore equipped for harbor protection, much as you suggested equipped with ASCMs and perhap UAVs. Right now, legally, such an organization should be under the Army. There is talk of the Army doing anti-ship but it hasn’t happened yet.

    As I see it:

    1. The torpedo idea would be the least costly and the easiest to implement. It would not sink the ship, but it would buy us time to organize and bring in other services to make the final kill (and take the credit).
    2. ASCMs on cutters while probably more expensive and complex in implementation, would offer the additional advantage of ASCM armed cutters in wartime.
    3. This would be a substantial commitment that would adversely effect Air Force, Navy, Marine, and Army units and still might not cover all possible targets.
    4. Adding a new organization to respond to this type threat is likely to be the most expensive. While there may be some opportunities to use personnel and locations currently in place, it would require additional training and personnel we don’t currently have.

    • Why not arm our WPC with a lightweight dual purpose torpedo? You could also work to integrate the future Sea Venom missle onto the Cutters and HH-65 also.

      • As to a dual purpose torpedo, of course the WPCs have not need of the ASW capability unless they happen to see a periscope. As far as I know the USN light weight torpedoes can be used against surface targets, but perhaps reprogramming a few for the CG might be feasible and we might convipnce the Navy that the CG is just a good place to store war reserve shots. We certainly aren’t likely to use many of them.

        On the other hand dedicated anti-surface torpedoes might be cheaper since the torpedo would not need to withstand pressure at great depth and homing would not need to deal with three dimensions.

    • Agreed, mostly.

      I think nothing we have now can be modified to become effective. To truly address this threat, new (drastic, some would say) programs/systems must be employed.

      I think your 4 possibilities are right on, and even listed in correct order in terms of effectiveness and ability to implement. I’d probably add another between point 1 and 2: Put a pair of attack helicopters with each MSST/MSRT, so there would be suppressive fire to protect the operators from MANPADS, RPGs, and small arms fire during deployment. (I think while a large merchantman provides the opportunity for a large group of armed terrorists, it seems unlikely. Somali pirates take over merchants with 2-3 people. Likewise, terrorist attacks seem to be trending towards smaller and smaller cells – usually just one or two people now. Still, a sophisticated attack with a WMD on a merchantman [“worst case scenario”], we could see 16-20 terrorists, perhaps 30. Still manageable for a strong boarding team, as long as they have some suppressive fire support to get aboard.)

      And just one point of clarification: My comments are somewhat about penetrating the hull. As we discussed above, the most-certain way for a quick, non-repairable (by terrorists afloat) mobility kill is to flood the engine room. The penetration must be at the right spot though. Any gunfire/missile/torpedo system would have to be targetable to the engineroom or steering gear.

      For missiles, this means an E/O seeker with command guidance. (A TOW missile launcher, surplus to the Army would be a great possibility and certainly would fit on the footprint of an 87′ or even smaller craft – just mind the back-blast.).

      Gunfire is just not practical. The vessels the CG has with large-enough caliber weapons are not usually going to be available due to deployments, repairs, or even crew availability if in port.

      The torpedo solution is by far the best. Wire-guided at short range it will be very targetable. It will engage the target at or below the waterline causing the desireable flooding. And it is the least obvious to the enemy that an attack is underway, diminishing their countermeasure ability. Even then, if they steer away, the command guidance would still allow prosecuting the attack.

  6. Is it possible to aim a burst of 57mm to hit the same spot? Perhaps the rounds would chew through the unarmored plates until some of them reach the vital parts of the engine room.
    Although the engine block itself is quite strong & located below the water line, you do not have to destroy the block to shut down the propulsion. In the space above the engine would be intercoolers, fuel polishing or heating equipment, and plenty of electronics.
    The space above the rudder would have hydraulic lines & electrical equipment which would also be vulnerable.

    • Getting a shot to pass through a single previous hole is certainly going to require a lot of luck, but perhap repeatedly shooting at the same spot from short range might open up more than a 57mm hole. Then you have to hope you get lucky. Sometimes you have to do that, but you can’t plan on being lucky.

    • Considering the number of rounds on the Mk.110 mount, this is certainly a possibility. They won’t have to go through the same exact hole. Assuming there is a double hull and one compartment between the outside skin and the engine space, a 15-30 round burst would likely accomplish this.

      An additional aid would be using a delay fuse on the ammunition to ensure the blast occurs at maximum penetration depth.

      Good points that the engine block itself does not need destroyed. Another problem with this type of attack is the many designs of potential attacking/rogue ships.

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  10. There is no technical reason that the NSC and OPC could not be redesigned and refitted to use the. Navy 5″ gun. Also the ammunition fired should contain a mixture of. AP , HE and Incendiary. Even the .50 caliber machine gun can fire A combination of Tracer, AP and incendiary. If you can’t sink her set her ablaze. If your looking for plunging fire, perhaps adding the old over/under mount that paired a .50 machine gun with a mortar. The patrol boat could stay off wither side of her bow and drop in rounds while the Cutter could approach from the rearr and engage the steering controls.
    Anyway,who was the dumb as*hole who approved the design of puny .57 mm as the main deck gun. Just what were we hoping to accomplish with it?
    Like the corvettes, DE and DD of the navy we need a decent main gun and with anti ship missiles or torpedoes. However they need to be there already mounted.

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