Showing posts with label Destroyer. Show all posts
Showing posts with label Destroyer. Show all posts

Sunday, 1 September 2013

August 2013 Thoughts: Ballistic Missile Defence


Ballistic Missiles are not a new threat any more, they have been a part of warfare since the V-2 first roared into the sky on a pillar of fire, smoke and anger at a world which refused to fit a dictator’s vision for it. Ever since that event the evolving forms of ballistic missiles have maintained a sort of sinister hold on the world and the public’s interpretation of international relations & global strategy. Even today the debate about them and their role as the method of delivery for Britain’s strategic deterrent; the only thing that cannot be doubted is there effectiveness as a method of delivery – in fact though the arguments for it’s continuation and the construction of a new class of Ship, Submersible, Ballistic Missile, Nuclear Powered (SSBN) to succeed the Vanguard class. However, whilst this funding is rightly being spent on this strategic deterrent; the procurement of a defence against these weapons is stagnated. 

Which is a problem as Britain has a lot to defend, and a lot to defend it against: America is not in range of Iranian missiles but the UK is, furthermore more nations are procuring them and as that happens there becomes greater risk of them falling into the hands on non-state actors (e.g. terrorists) who may not be deterred by theory of Mutually Assured Destruction (MAD) which works so well against state actors. Whilst such a system might not be the most deadly weapons a terrorist could use, the very ability to get hold of one and fire it would inflict a tremendous level of terror. This is a risk magnified when states with such weapons have internal conflicts erupt as it’s difficult to predict not just the winner, but who will control the weapons and what will happen to them. This is why it’s necessary to do a two pronged approach to Ballistic Missile Defence, maintaining the deterrent but also developing an intercept capability – for which there are multiple options.

The proposed defences against ballistic missiles are varied, using a laser fired from a Boeing 747, land based missiles (of course) and sea based missiles – the difference between all of them being the point  at which the aim to intercept the missile. The Boeing 747 is orientated dealing with the missiles in, although it’s still under development; the ground based missiles are mostly focused on either terminal or mid phase interception, and the sea based missiles are theoretically boost phase and terminal phase – but they are mainly focused on the latter. The sea based systems are currently the most proven, in that one of the systems, Standard Missile 3 (SM-3)/AEGIS,  have been used to intercept satellites & practice targets successfully and are based on a legacy design which is as close to a proven program as can be found in modern defence systems[1]. So which system would best fit Britain; well conceivably any of them, but as there are now existing land based long range air defence batteries within the UK armed forces, and the costs are still mounting on the airborne laser…furthermore there already in service capabilities which could be built upon.

For the sea based system there are the Type 45 Daring class Area Air Defence (AAD) Destroyers, these have two radars, a long range search radar, the S1850M  L-Band system which provides it with excellent long range warning; but it’s the other radar which is something special. The Royal Navy (RN) has possibly what is the best radar in service in the field of sea based Ballistic Missile Defence (BMD), the Sampson radar, it is a two plane solid state phased array radar that rotates 30x a minute so that even without electronic steering of the beam (which it can do) no sector will escape scanning for more than a second. Therefore it builds a very accurate image of the world around it; well the over half a million kilometres squared. So with such a set of radars mounted on a vessel which also includes a very stable power supply and an extremely powerful set of computers; the RN would seem to have Britain in a position half way to the finish line.

There are problems though, the Type 45s are fitted for but not with 16 Strategic length Vertical Launch System (VLS) cells[2] – these are the length required to support a missile big enough to intercept Ballistic Missiles. There are two options for that VLS that would be compatible; the European Sylver A70 and the American Mk41/Mk57 VLS – however these systems themselves generate a further problem, as each system comes with it’s own range of other missiles that can be operated from it – not just BMD missiles, but also cruise missiles and more.

The Sylver A70 VLS would seem the obvious choice as it is the A50 which the Type 45s are already fitted with. However, it is only in service with one navy on one class of ship, the French FREMM Frigate, meaning that it isn’t widely tested nor widely resourced – making it more expensive long term as parts will be more specialist to procure. The biggest problem though is the fact that the BMD system that goes with it, doesn’t matter if it’s called Aster 45 or Aster 30 Block 2 BMD is still under development and everything is categorised as ‘potential contributor’ – it could be a really good system, but by the time it may enter service the Type 45s could have already served half their expected life… However, until then the RN could share a the 500km/270nautical mile range SCALP Naval (the surface launched version of the Storm Shadow which is expected in service with RAF Typhoons in 2014 – it’s already in service with RAF Tornadoes) to provide them with a tactical land attack capability. In summary, it’s a lot of promise, a lot of potential, a very big chance to spend money to not get much back…

In contrast the Mk41/Mk57 VLS (Mk57 is supposed to be its new & improved successor, it’s currently looking like a Fairey Albacore situation, better than its predecessor but not by enough to be really desired) is possibly the widest employed VLS in service today, serving 13 countries & 22 different classes of ship. Furthermore, it’s the system which has always been given as what the Type 45 had the space for – something which is not just due to its credentials for launching the SM-3 BMD system, which as has already been discussed is in service with two nations, has shot down satellites (a very useful secondary capability considering the reliance modern warfare has on them) and is in use by two navy’s with another looking into it, so the RN would not be left to carry the costs on its own…and there would be other nations with which to pool supplies in emergencies. The reason it was in the frame from the beginning was because the Mk41/Mk57 brings flexibility, it brings the RUM-139 Vertically Launched - Anti-Submarine Rocket (VL-ASROC) which can assist tremendously with Anti-Submarine Warfare (ASW) as when the helicopter runs out of torpedoes, instead of it having to fly back and loose the target in order to reload, the ship launches the torpedo using the data from the helicopter. Most importantly though the Mk41/Mk57 is the system that launches the 1,700 km/900nautical mile ranged Block IV Tomahawk cruise missile (that’s over 3x the range of Storm Shadow), a system which is already used by RN submarines. Simply put the MK41/57 would turn the Type 45 from an AAD into a General Purpose Missile Destroyer (GPMD).

Even if 16 cells are all that can be fitted the Mk41 VLS would be useful, as 16 cells could be translated into 6 SM-3’s, 2 ASROCs and 8 Tomahawk TLAMs which would be a very good addition to the Type 45’s already capable 48 SAMs; something which could also be changed should CAMM replace the Aster 15, after all four CAMM can fit in the same cell as one ASTER 15 meaning the missile load could become 37 Aster 30, 36 CAMM for the same 48 cells. However, this would not be it’s only form/load; if going to sea as UK Patrol ship (where the vessel would be unlikely to use TLAMs) the destroyer might be loaded as a BMD/ASW vessel with 10 SM-3s and 6 ASROCs alongside the 37 Aster 30s & 36 CAMMs; or alternatively she might be part of a task group being sent to launch a strike, in which case whilst one vessel might carry 12 SM-3s and 4 TLAMs, the others would carry 16 TLAMS[3]. Finally, there is the black scenario – a RN destroyer operating in the pacific far from resupply uses up all it’s missiles, with a MK41 VLS that’s already fitted for SM-3 missiles she could be reloaded (conceivably with minor modifications) with SM-6 missiles the new standard missile air defence system. It’s not a full proof solution, but it provides an option for worst case scenarios. This is why that while Sylver does offer some capability, the Mk41 beats it as a strategic VLS for procurement by the RN because of the diversity of weapons.  

The radars & design make them perfect vessels for BMD – which would give them another role they could excel at; the choice of VLS could make the Type 45s so much more. The Sylver locks it in, whereas the MK 41 allows it to evolve. Furthermore it would set a precedence and maybe that would help with future arguments over escort numbers, because with 6 ships for AAD/BMD/Strike it could well seem sensible to expand building plans and at least provide more extensive numbers for AAD & Strike; perhaps increasing the Type 26s, or building a lot more general purpose Type 45s. Britain is an island nation, so often that is left as some de-facto reason to invest in a navy; not in this case though, the sea is Britain’s strategic depth, we don’t have Marshal Winter we have Admirals Storm & Wave – BMD making use of that depth is the best way to provide Britain and our overseas territories which depend upon us (as we benefit from the resources within their domain) to provide security for Britain.

Further Reading:                             





[1] The system is already in service with the United States Navy and the Japanese Maritime Self Defence Force, with Turkey considering it.
[2] This would be in addition to their 48 Air Defence length Sylver A50 Cells + some sources have said in the past it was up to 24 cells – whatever the truth, between the current VLS and the superstructure where currently the Harpoon SSMs would go, but conceivably they could be moved, and in fact two of the class already aren’t fitted with them.
[3] if just 3 Type 45s were present that would be 44 TLAMs or more than the collective TLAM load out of the RN submarines

Friday, 24 May 2013

May 2013 Notes: Using Ballistic Missiles to Kill Ships


Reason for writing:
http://www.strategypage.com/dls/articles/Chinese-Carrier-Killer-Works-5-6-2013.asp 
http://thediplomat.com/the-naval-diplomat/2013/05/03/what-modern-militaries-can-learn-from-battlestar-galactica/

Context:
Pretty much every generation since 1900 has had a new thing come along which has caused commentators to declare the surface warship was dead and should no longer be built; although since 1945 a variation has appeared where by some merely say it’s the end of the aircraft carrier…in reality the situation is definitely not so black and white.

Key Words/Phrases:
·         VLS: Vertical Launch System
·         UCAV: Unmanned Combat Air Vehicle, in this work is mainly used to refer to the   X-47 - The currently under development, but conducting carrier deck operations and flying, Unmanned Combat Air Vehicle, the X-47 is the future of stealth strike & reconnaissance; hence there is no coincidence that it looks like a mini B-2 bomber.
·         ABM: Anti-Ballistic Missile
·         EMP: Electro Magnetic Pulse
·         MaRVs: manoeuvrable re-entry vehicle, it’s a warhead which can manoeuvre upon re-entering the Earth’s atmosphere.
·         General Exchange – it’s not an officer, in this work the phrase is used to cover a scenario where by the ballistic missiles are fired by both sides at each other’s strategic targets…the very scenario which causes such fear and which helped to keep the Cold War coldish.
·         Humit: Human Intelligence – spies or maybe special operations personnel camping near the enemy ports to monitor and report their movements in detail.
·         Signit: Signals Intelligence – what is gleaned from reading enemy communications.
·         Intit: Internet Intelligence – what is got from reading facebook, blogs, twitter updates… this might be just from some random person walking along writing a status “just saw a big grey ship going out to sea…huh, it was Bitchin” tells everyone that a ship is moving, this sort of thing is very difficult to stop, and can be very useful. Sometimes also called SoMeit meaning Social Media Intelligence…but Intit sounds better.

Key Points:

·         Limitations of weapon: Ballistic missiles are not infallible; they are in fact rather large rockets, possibly considering their purpose is to go bang, more accurately rather large fireworks…that’s not to say they can’t be best of option available for something’s though[1], but for the Anti-Ship role there are issues:

o   Warhead: Nuclear, conventional or other? If it’s nuclear then a nation which uses it is almost certainly starting down the path to a general exchange, but if it’s conventional then the accuracy required to even hit the largest vessels afloat at such ranges would be virtually impossible to attain at current levels of technology. The other is EMP, which is actually possibly the most sensible as if fired it would in theory (something which has to be underlined) be less likely to result in a general exchange, it might well damage or even overload & destroy communications/electronic equipment and would certainly knock out any aircraft any task group had in the air… the problem is that to be effective against the ‘shielded’ systems of ship that such a weapon would have just as big an impact on any friendly forces in the area, so instead of it being a game changer it would be more of a game reseter with victory going to whichever side recovers quickest with the advantage of course being to the side which knew it was going to happen. All in all though, even an EMP weapon could result in the setting off a general exchange…a hefty price to pay for the tactical advantage that could possibly be bestowed by temporarily damaging the enemy task force.

o   Liquid or solid fuel? this is important, solid is more difficult to make requiring a greater degree of industrial and scientific force, but liquid fuel is often more dangerous to handle and places limitations on the missiles as its often very corrosive meaning they cannot be left fuelled, so have to be fuelled immediately prior to launch, delaying it. 

o   How manoeuvrable is it in flight? Can it be given mid-course guidance or will a splatter gun effect have to be employed? Now whilst reports have varied, but it is claimed that the MaRVs have some capability to be given course corrections in the case of the DF-21C (CSS-5 Mod-3)[2] if it’s true it’s brilliant, but at speeds of Mach 10 a minor error could be colossal and its hard to see how terminal guidance radar would work with the amount of heat generated by the air-resistance during re-entry. The solution if such a capability is real[3], is most likely that these MaRVs go slower so as the reduce heat; in which case they lose the crucial advantage of ballistic missiles which is their sheer speed and the difficulty that presents in dealing with them[4], or alternatively the terminal guidance is based on telemetry received from another system by a link transmitting/receiving from the ‘cold side’ of the MaRV – although such a system would seem to be purely a theoretical construct at present time.

o   Range, the DF-21 is not an inter-continental ballistic missile system, it’s a theatre ballistic missile system, which means there is limited strike radius – in the case of this system its claimed to be roughly 3,000km or 1,900mi


The range of the DF-21


·         Limitations of locating target: it’s not just the weapon system though which will be causing issues.

o   Ships move – it’s obvious right, but in 45mins an 18knot Royal Navy amphibious task group will have moved 15miles from where they were when the missile was launched, it’s not like the land targets or large exposed troop concentrations that are the traditional targets of ballistic weapons…these targets are not unshielded and could move out of the way. A carrier battle group moving at 32knots could have moved nearly 28 miles; in any direction, this makes accurate targeting analysis and mid-flight course correction a necessity, because even a nuclear bomb at its most powerful doesn’t have a big blast radius.

o   The ocean is big, really, really big; the Soviet government found this out when they threw RORSATs, TU-142 Bears[5], IL-38 May’s, a huge submarine fleet and more than likely a hefty Humit & Signit effort at it… and still the USN and other NATO forces eluded them more often than not. The Chinese are investing in lots of satellites, UAVs and more than likely other systems as well – added to Humit and Signit, there is now Intit. All these things could well be deployed, but so can false leads, jamming, smoke pots and probably has other options as well…

o   They don’t make it easy, even when ships are being tracked they can speed up/slow down, zig zag, in fact throw in every option they want to, including choosing the time & place of when they move into the missiles strike radius

·         Problems of command & control[6]

o   Information comes in, this weapon system is not going to be a local command one (there are simply just too many strategic factors for even a theatre commander to be given the keys), and all the time it takes to make the decision as to launch the data is going to be degrading in accuracy, meaning at a certain point it becomes it becomes pointless to launch.

o   Furthermore the system is going to depend upon a vast array of data, and a very robust network to bring all that data from such disparate sources together…these are both things which can be attacked.

·         Diplomatic/strategic problems

o   Launching a Ballistic Missile is launching a Ballistic Missile; it’s not a road which can be easily travelled in reverse. Even in the post-Cold War era of dΓ©tente, the Russians were not accepting of a planned American conventional ballistic weapon for quick strikes[7] - during a war fighting scenario, any launch runs the risk that the US president (who under such circumstances would be under already enormous strain) might not be a strong person, and might have hawkish advisors advising them to immediately launch their weapons in reply… quite possibly leading to the scenario of failing to destroy an American carrier battle group (or for that matter destroying it) results in the destruction of pretty much the whole country…not exactly the scenario either Sun Tzu or Alfred Thayer Mahan would advise.

o   Furthermore there is the fact that launching such a weapon may get a response from an unintended target, for example consider the scenario, China launches a spread of DF-21s against a USN force in the Indian Ocean that has been detected, a) the missile’s flight path will lead to protests being filed by even friendly Burma, Bangladesh will also file a diplomatic protest, India because of recent flares up exacerbating long term disputes over territory (and operating at heightened state due to the conflict going on around it) sees the missiles and thinks they are an attack on it so immediately launches a reply in kind – again leading to a general exchange.

·         Evolution of target; the trouble is American carrier

o   Long range stealthy UCAV, the X-47B[8] is the one which is turning all the heads at the moment, it looks like a mean mini B-2 Spirit bomber, but this aircraft is far more than that. It has an un-refuelled range of 2,100nm or roughly 3,889km; but its capable of doing air-to-air refuelling, this means that even if they were dispatched on a one way trip these aircraft would allow the USN’s aircraft carriers to start hitting the targets whilst they are well outside the range of the DF-21 or in fact any of the other systems. Refuelling would enable them to loiter, waiting for the vehicles to move from their hardened bunkers and head for their launch positions so they can take them while they are exposed[9]. So whilst the missiles might be relatively cheap in comparison to a battle group, the launch vehicles and more importantly the personnel would not be so cheap & easy to replace…destroying enough of them would undermine if not put out of commission the whole system – the often most effective method of stopping an attack is not hitting the weapons, but the source, the ability to shoot down the weapon is important because things go wrong and surprises happen…but attack at source is  truly the best form of defence.
o   Laser defences[10], ‘missiles are cheaper than ships’ is a constant refrain when talking about the future of warfare, usually followed quickly by prediction of massed (thanks to an integrated network of systems) saturation attacks decimating fleets… well lasers are even cheaper than missiles, and whilst at the moment they are limited to blinding missile sensors in some versions, or in some of the more recent larger systems shooting down UAVs and burning small boats. They are advancing just as quickly as missile technology is, and as ships all by virtue of necessity carry very large power generation systems, the future of laser weaponry is looking good…after all as long as the ship has power it will be able to fire lasers, and as they ‘move at the speed of light’, saturation attacks could well have to change. More importantly there is the option (with even the current generation) that the laser could be used to provide a more accurate targeting of the inbound enemy weapon, thereby smoothing the interception and increasing chances of it being stopped before it could do any damage.


A USN produced graphic explaining the current laser system being tested

o   ABM/ASSAT weapons, for the USN, IJN and the RAN the SM-3 & Aegis is the primary system for ABM work[11], it has a ceiling of over 100 miles and a range of over 270 nautical miles meaning it can provide protection over an area roughly 500x the Area of Greater London. The USN is aiming to put this system on every one of their Arleigh Burke class destroyers – and every other AEGIS equipped vessel they have; this means that multiple escorts in any task group will have the capability to defend it should attack at source fail or should they be caught by surprise… it also makes the job of the attacker that much more difficult as they have to factor in the likelihood of success into their use of a ballistic weapon, the more of those fire the greater the chance that a general exchange might be brought about.

Missiles being fired by Ticonderoga class cruiser CG 69 USS Vicksburg, the Flight I Arleigh Burke class destroyers DDG 64 USS Carney & DDG 68 USS The Sullivans and the Flight IIA (5”/54 variant) Arleigh Burke class destroyer DDG 80 USS Roosevelt

Furthermore, whilst the Aegis ships armed with SM-3s in the Pacific fleet might well consider the DF-21s and their kind to be their primary targets in any conflict, the ships in the Atlantic fleet might well be used to target the very satellites which would be used to hunt their Pacific brethren. For such a mission the system has already been demonstrated against a satellite which was 133 nautical miles(a little over 153 miles) above the earth moving at roughly 17,000mph[12], this is important because the majority of satellites are maintained in the Low Earth Orbit…and even in that most of them are within 90 minute range (Meaning they complete an orbit every 90minutes) or roughly 100miles above the earth, now whilst communication satellites and GPS systems are as a rule in higher orbits, intelligence & reconnaissance satellites (as a rule) are in the lower orbits putting them in range of SM-3.

Explaining the Orbits

Points of Interest:

·         In his 1925 book “Winged Defence; the development and possibilities of modern air power - economic and military”¸ Billy Mitchel proclaimed

“Surface navies have entirely lost their mission of defending the coast because aircraft can destroy or sink any seacraft coming within their radius of operation. In fact aircraft today are the only effective means of coast protection. Consequently, navies have been pushed out on the high seas. The menace of submarines from below and aircraft from above constitutes such a position that the surface ship as an element of war is disappearing. Today, the principal weapon in the sea is the submarine with its mine layers, gun fighters and torpedo craft.

In the future, campaigns across the seas will be carried on from land base to land base under the protection of aircraft. Expeditions across the sea such as occurred in the World War will be an impossibility. Water spaces between land bases in the northern hemisphere are very short. The space from America to Asia is only fifty-two miles across the Bering Straits and across the Atlantic it is scarcely more than four hundred.”[13]

Now leaving aside invading Siberia from Alaska and the logistical nightmares that would entail, it was an interesting claim, and supported by many such as Trenchard of the RAF and the Italian Air Power theorist Giulio Douhet… it was thinking like this which underpinned many decisions in the 1920s, unfortunately for the theorists whilst some of their arguments were later proved in the course of World War II, they were disproved on many more of them, including the notion that ships would only not be able to fight where land aircraft dominated… the evacuations of Dunkirk, Crete and many others all showed that whilst casualties would be taken, operations could be accomplished.

·         What drives the size of aircraft carriers, and their capability is the air group – aircraft are getting bigger, because more is expected of them and so they have to include more equipment as standard… this means to accommodate an air group of even the same size as a previous aircraft carrier, the ship will need to be bigger… and that’s before factoring the fact that an aircraft carrier will at minimum see two generations of aircraft fly from its decks, which means it needs to factor in some space for future proofing…otherwise the money will be wasted after just a decade and a half of service. Furthermore, when talking about an aircraft carrier it is necessary to consider the ship, a) may be any kind of large aviation ship (i.e. an LHA or LHD[14]), and b) it’s air group/role within the Task Force. Why is this point of interest to this report?

Well simply put the aircraft carrier is often set up as a ‘straw man’ for the arguments, or others say that these weapons mean that aircraft should be spread around more smaller aircraft carriers…these notes are not weighing into that argument, but to say that such points are missing the point, these missiles if used are not likely to be used against a Carrier Battle Group, more likely an Amphibious Task Group, it would be a very sceptical person who could believe  there is no coincidence that the DF-21’s range is advertised at being enough to provide support to forces operating within the second island chain[15]…and Amphibious Task Groups even launching assaults from beyond 10 nautical miles are still a lot more predictable in area than Carrier Battle Groups...and to a certain frame of mind, whilst bombing can damage or destroy, its marines & soldiers when landed by a navy which recapture or capture.

The First & Second Island chain

Summary:

The reality of anti-ship ballistic missiles is it is they which are really the white elephant, not the aircraft carrier or the surface warship; they are drain on resources, as they will have to be defended, maintained and manned… all things which will cost money, but unlike the aircraft carrier they cannot be used – for if they are used then the likelihood of a general exchange depends upon the thinking of the least well informed/least prepared government leader whose nation is affected by such a launch. There is the very real possibility that success or failure would both lead to massive retaliation… under these circumstances, whilst defences must be built against such systems (as failure to prepare will certainly lead to failure, and it isn’t an impossibility that actually taking the step/running the risk of firing an Anti-Ship Ballistic Missile, and it then failing to sink its target could lead to leadership change in the country that fired it/peace talks); the reality of future conflict is more likely to involve dealing with attacks by incredibly sophisticated cruise missiles/UAVs (frankly the line is starting to blur between these two systems[16])… the good thing for navies is that defences that can deal with ballistic inbounds can most likely also give a very good effort against the more likely threats.




[3] There have been other systems built with a terminal guidance radar capability, but this was a radar designed to fix land positions to provide accuracy – i.e. where the surface wasn’t flat an essentially featureless, the difference in radar return between an Ultra Large Crude Carrier (ULCC) and an aircraft carrier is not that much.
[6] This is why the Battlestar Gallactica article is worth reading, it makes some good points about the problems of network centric warfare and over-reliance.
[7] For more information about the Prompt Global Strike Program; http://www.nti.org/gsn/article/us-brass-reviews-prompt-global-strike-mulling-submarine-fired-arms/, www.fas.org/sgp/crs/nuke/R41464.pdf‎, www.fas.org/sgp/crs/nuke/RL33067.pdf‎ and http://breakingdefense.com/2012/12/17/pentagons-global-strike-weapon-stuck-in-limbo-congress-fears-a/
[9] This could even be arranged to happen when the UCAVs are over the target, by the simple expedient of a carrier battle group ‘allowing itself’ to be seen within the strike range, under those circumstances the Chinese government would either have to order a firing of the weapons or accept a damaging loss of face when images of the carrier conducting operations from within their ‘no-go zone’ get beamed around the world.
[11] Its Wikipedia but it’s source list is a good place to start looking for information about this system http://en.wikipedia.org/wiki/SM-3_missiles, interestingly enough the RN’s Daring class AADs have an excellent radar for this role (the Sampson System) and are fitted for the large VLS (the MK41) necessary for them to be able to carry the SM-3 (or Tomahawk cruise missiles, should that be wished) but are instead fitted with the smaller A50 Sylver VLS, which is what limits them to the Air Defence role rather than a more general purpose role – for more info please read http://amphibiousnecessity.blogspot.co.uk/2009/06/whatever-happened-to-type-45.html, http://amphibiousnecessity.blogspot.co.uk/2009/02/type-45-paamssea-viper.html & http://amphibiousnecessity.blogspot.co.uk/2008/12/destroyers.html .  
[13] (Mitchell 1925, xvi)
[16] This will be the subject of another notes in future.