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

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.

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

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.

Conclusion: 

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.