Successor Submarine and Alternatives

There are countless things that can and should be said about the much discussed plan for the sustainment (not replacement, as is incorrectly said all the time) of the Trident missile system.

Overall, there seem to be agreement on the fact that submarines remain the best platforms for the deterrent, with no one questioning the long demonstrated rationale of moving away from an Air Launched deterrent with fleets of strategic bombers and tanker aircrafts. No one, unsurprisingly, is arguing for a solution made up by silos on land. There’s a current that calls for outright nuclear disarmament, but this option in my opinion is not even worth exploring, and then there is the famous “review of the alternatives” sponsored by the LibDems.  

I thought I would write my own quick review, mostly technical, of the possibilities of adopting an “alternative” and ideally cheaper submarine-based deterrent.

In the past, I wrote a wider analysis and report about the Trident situation, including a comparison of national Nuclear Doctrines, which shows, for example, that France’s nuclear policy is one of the most aggressive ones, while China’s official position is, at least for now, remarkably similar to the UK’s one.

That earlier, large review remains valid, so it is worth a look into, here.

First of all, what exactly are we talking about?

There seems to be a quite widespread ignorance of what program the MOD is currently trying to tackle. The heated debate over the nuclear deterrent has contributed to bring politics all over the matter, making it confused and painting a picture of the situation that is often unclear at best.

The nuclear deterrent is composed of these main components:

Trident II D5 is the missile/weapon system. It is not going anywhere at least until 2042, when it -might- be replaced by a new missile development, indicated, i don't know how reliably, with the name Trident II E6. With the recent test launch from HMS Vigilant, the Trident missile has logged in 143 consecutive succesfull, flawless launches. So it makes sense to assume that, more than a replacement, the next missile will be a technology refresh largely based on the already available material. In any case, what the UK is wrestling with at the moment is NOT a replacement for the Trident missile system. 

For the UK, Trident II is a bargain, as it purchased the rights to 58 Trident missiles under the Polaris Sales Agreement (modified for Trident) from a jointly maintained "pool" of missiles that arms both the british and the US Atlantic SSBN fleets. These missiles are fitted with UK-built warheads and are exchanged when requiring maintenance. Under the terms of the agreement, the United States does not have any veto on the use of British nuclear weapons. Some of the Trident missiles originally acquired have been fired in test launches, so the Vanguard submarines have never (and will never) have all of their tubes filled with missiles.

In fact, while the theoretical capacity of the four Vanguard-class submarines is 64 missiles and 768 warheads (16 missiles for each submarine, each missile carrying up to 12 warheads), only 58 missiles were leased and some of these have been expended in test firings. The UK leases the missiles but they are pooled with the Atlantic squadron of the USN Ohio SSBNs at King's Bay, Georgia (previously the UK maintained its Polaris missiles in-country).

  

The nuclear warheads themselves are instead UK-made, from design to assembly to maintenance to preserve the independence of the deterrent.  This work is done at the Atomic Weapons Establishment (AWE) in Aldermaston.

The nuclear warheads carried on Trident are also due to live on for many more years, with a replacement not envisaged before “the late 2030s” and possibly further onwards, out to 2042, after in 2010 the UK accessed technology being used by the US to extend the life of their own warheads and increase their accuracy to enable more effective targeting of hard and deeply buried point targets. 

The US warhead is the W-76-1, and the british one is presumably a national development of said weapon.

It is anticipated that developing a new warhead when the current ones will have reached the end of their safe and useful life will cost 2 or 3 billions. As part of cooperation with France, the two countries are working together to ensure the safety and effectiveness of their nuclear warheads: considerable savings have been achieved by deciding that the complex computer simulations needed to ensure the safety of the nuclear warheads (since live nuclear tests are notoriously banned) will be carried out in France, at Valduc, near Dijon, from 2015 onwards. A new, modern facility is being prepared for this, under the name EPURE, specialized in the study of the complex hydrodynamics connected to a nuclear explosion (solid materials behave like liquids when subject to the extreme levels of pressure and shock of a nuclear detonation). The british Atomic Weapon Establishment will take on the role of developing new technology in exchange, with the creation of a Joint Technology Development Centre which will develop advanced instruments for EPURE itself. This has relieved each country from the need to invest several more billions. The UK, for example, would have had to invest billions in the Hydrus, a new hydrodynamics test facility at AWE, that now will not be.

As a consequence of all these considerations, the expense for a warhead replacement is out of the current planning horizon. 

The Vanguard-class SSBN are what the current "Trident replacement" is about. It is indeed a submarine replacement program, better known as "Successor Submarine", or Successor SSBN. These four huge vessels have spent at sea all their life, being hard worked to sustain the Continuous At Sea Deterrence Posture. HMS Vanguard, the first in the class, entered service in 1994, and the last SSBN of the type entered service in 2001: in theory, by 2026 their operational life would be over.

Planned to live 25 years, they will now be life-extended by a considerable number of years, with HMS Vanguard having its out of service date moved from 2019 to 2028, and the others following.

Further life-extension is deemed too expensive and risky to make sense. Being only four in the class, these submarines have been worked harder than their American Ohio counterpart, which will start being replaced into the 2030s.

The Successor Submarine is the program at hand. The idea is to build a new class of SSBNs which will operate from the same shore infrastructure (keeping any need for modifications and enhancements to an absolute minimum) and employ, at least for the first part of their life, the very same missiles and warheads now carried by the Vanguards.

The expenditure for new missiles and new warheads, if and when these will be needed and procured, should be kept separate from the submarine part of the deal, as it will be spread over decades into the future.

Successor Submarine – the current plan

At the moment, the plan is to build a fleet of 3 to 4 new SSBN submarines, which will carry the Trident missiles. These vessels will be slightly larger than the current Vanguards, but will use the same shore infrastructure. They will carry 8 launch tubes, in two rows of four, down from 16 on the Vanguards. They will use a new, safer nuclear reactor for power, the PWR3, which is partly responsible from the size growth.

It is intended that the new SSBNs will largely derivate from the Astute-class SSNs: in particular, the two classes will share the same control systems, the same tactical torpedo system and the same sonar suite, making the training of crews similar enough to enable easy transfers from SSN to SSBN and back as necessary.

The new SSBNs will thus have a very potent battery of 6 torpedo tubes and room for 38 torpedoes and Tomahawk missiles in addition to their nuclear arsenal. They will also have a formidable sonar suite, possibly the best in the world, and they will offer the benefit of great commonality with the attack submarine fleet.

The Trident launch tubes module is being jointly developed with the US Navy, to keep costs down as much as possible. This Common Missile Compartment is composed of blocks of 4 launch tubes each, with the new US SSBN planned to have 4 blocks, and the british one 2 blocks. Work on the CMC has been smoothly going on since 23 December 2008, and the maturity of the design is now very high.

It is intended that the overall size of the nuclear deterrent will shrink: until the SDSR 2010, the Vanguards would go to sea for patrol carrying 48 nuclear warheads, distributed unevenly on up to 16 missiles, offering some “flexibility” in the Armageddon scenario, in theory making it possible to retaliate “proportionally” with combinations of between 1 to 48 nukes.

The Successor will only carry eight missiles, and a total of 40 warheads.

As a consequence, the total stock of nuclear warheads will shrink from around 225 to “no more than 180”, of which 120 (down from 160) would be available for operational use at any one time.

The combination of Trident missiles, a fleet of 4 SSBN and a proportionate stock of available warheads ensures that one submarine, loaded with live missiles, is always at sea, 365 days a year, year after year. Once at sea, the submarine is virtually undetectable and offers maximum survivability: so long as CASD is maintained, no enemy is in the position of whipping out with a pre-emptive strike the nuclear arsenal of the UK. Even if they hit and destroy Faslane and the submarines in port, at least one and at times two submarines will be somewhere out at sea, ready to retaliate in little more than 30 minutes: the time Trident takes to hit a target up to 10.000 km away. The ballistic range of Trident means that a submarine hidden in safe waters can relatively easily target anyone in the world to retaliate timely and assuredly.

For me, the Survivability and the Certainty of a nuclear retaliation option are the two decisive factors: a minimum credible deterrent, which is what the UK needs, must absolutely be:

-          Survivable: the enemy must not have the easy option of whipping out the british nuclear deterrent with its own first attack

-          Certain and Timely: the enemy must be in no doubt that a nuclear attack will be met, 100% of the time, with proportionate nuclear retaliation, from which the enemy must have no realistic escape.

If the deterrent cannot meet these two crucial requirements, it is useless. If the enemy can destroy the arsenal at will or defend itself from the retaliation strike, the enemy will not be deterred at all. If it is not Survivable and Credible, then it is better not to devote money to it at all.     

The current and future SSBN solution meets the above requirements.

The current Successor Submarine strategy:

-          Requires a new submarine class to be designed and built, but no new warheads and no new missiles for the time being

-          Makes best use of US collaboration and support, cutting costs while protecting independence of the deterrent

-          Ensures capability to continue mounting a Continuous At Sea Deterrence

-          Does not impact negatively on the availability of attack submarines for conventional Fleet roles

Alternatives?  

Lengthened Astute with 4 launch tubes: one option that has been mooted is that to build 3 or four more Astutes, inserting an additional module aft of the fin containing a single block of 4 Trident launch tubes.

Unfortunately, this solution is not at all easy and straightforward.

First of all, the current CMC block of four tubes in two rows of 2 sitting side to side won’t fit the beam of an Astute submarine. So the development work done this far would not be sufficient, as we’d have to design a module with the four tubes sitting in a row, one after the other, making the submarine quite a bit longer. 

Workers stand proudly inside the launch tubes of a quad-pack block built as part of the CMC effort

This is, in line of principle, not at all unfeasible: indeed, the US Navy plans to do exactly this on its Virginia class SSNs of the Block V, which have already been fitted with two large vertical tubes in the bow starting with the Block III vessels currently being built. These two large tubes, fitted with “six-shooters” frames holding each 6 Tomahawk cruise missiles, have replaced a more complex and less flexible complex of 12 single VLS tubes mounted on earlier submarines. The US Navy plans to develop, build and install a “Virginia Payload Module” with 4 large tubes into the vessels of the fifth production block. This Payload Module, with 4 tubes aligned to the submarine’s centerline, comes with a pressure hull that is 34 feet in the beam at the fore and aft extremities, going down to a 26-foot wasp-waist around the tubes themselves: this is because space was needed outside of the pressure hull to install the heavy, bulky mechanism of the hatches and additional ballast tanks, plus some unallocated space. An outer, non-pressure hull wraps up and completes the module, maintaining the Virginia’s hull profile and beam (34 feet). The length of the whole module is determined by the need to balance the considerable additional weight made up by the launch tubes and related machinery.   

On the Astute, the arrangement would have to be pretty much the same, since while the Astute has a larger beam (11.3 meters against 10+ for the Virginia) it is still not enough to make another configuration viable.  

A General Dynamics Electric Boats image, showing the Virginia Payload Module with its four large tubes, here fitted with a rack for 7 Tomahawk missiles each. Two further large-diameter tubes, even shorter and carrying only 6 Tomahawk each, are fitted, outside of the pressure hull, in the bow of the Virginia subs from the Block III vessels onwards. The VPM's four tubes offer greater flexibility than the bow ones as they can be accessed from inside the sub. The bow tubes, being outside of the pressure hull, cannot be accessed by the crew.

But, since an option does exist, why is this not a viable alternative Vanguard replacement for the Royal Navy?

For a pretty simple reason, which is the same main problem ruling out a Virginia-based Ohio replacement: the launch tubes fitted to the SSN have the same diameter of those fitted to the SSBN, but don’t have the same length. The difference in sizes between SSN and SSBN are not casual: the Trident missile is a big beast, and is 44 feet long (or tall, if you prefer, since it sits vertically in the tubes).

In an Astute submarine, the launch tube would offer at most 36 feet of useable length, so the Trident missile would suddenly need a whole new replacement that the UK would have to fund on its own.

The Virginia Block 5 will use its 4 large tubes to carry modules with 7 Tomahawk each, increasing the cruise missile load on the SSN up to 40, counting also the 2x 6 in the bow. Even more Tomahawk could be carried in place of torpedoes, and the large-diameter tubes are seen as a mean to future-proof the submarines, enabling them to employ, in the future, new missiles, unmanned vehicles, special forces gear, and other kit.  

The Virginia Block V, in fact, was immediately deemed unsuitable as an Ohio replacement solution: the US Navy envisions the new vessel as a replacement for the 4 Ohio submarines that were modified into SSGNs. The US Navy in fact is aware that a boat as ambitious and expensive as an Ohio is not going to be affordable in the future, and it has been deemed more effective to replace such SSGNs with boats that have obviously far less firepower (a converted Ohio can carry some 66 special forces operators and a load of Tomahawks that can reach the amazing figure of 154 missiles) but that will be more numerous, and will overall add more capability to the fleet for an advantageous pricetag.

The current Ohio SSGNs will be retired from service starting in 2026, so the US Navy is obviously already at work over the Virginia Payload Module, with the aim of starting the building of the first Virginia Block 5 in 2019.

It is probably not technically impossible to fit Trident missiles into an Astute, but this would have a dramatic impact on design and performances of the submarine, as it would be necessary to gain a good 8 feet in height over the back of the submarine, and this would impact weight, hydrodynamics, stealth when surfaced and, crucially, it would have a very bad effect on acoustic, making the submarine a lot more noisy when underwater, and thus much easier to detect, a problem typical of certain Russian SSBNs, such as the Delta IV, which very evidently show such a hump behind their conning tower. 

Something like this would be the result of trying to fit Trident II missiles into an Astute hull. This solution would be relatively easy and cheap, but would ruin the submarine's performances, making it slower and louder underwater. 

The Americans, unsurprisingly, absolutely did not want to walk this path with their replacement SSBN and with the Virginia Block V.

While technically feasible, it is a very bad solution for a lot of reasons. The savings would be negligible, and the submarine coming out of this solution would be, basically, a flawed design, using a solution that everyone has abandoned because of its defects.

If we went with the shorter tubes and tried to design a new ballistic missile to fit into said tube the costs would skyrocket, and the UK might well not have the industrial capability to develop such a complex ballistic weapon on its own, since there is no real previous experience to build upon.

Arguably, the Astute SSNs should have been built with large vertical tubes, but like with the Virginia Block V, these should not stretch out of the carefully designed hull profile, and thus would be not be Trident tubes. 

The Virginia Block 3 bow in direct comparison with the bow arrangement on submarines of the earlier batches. Best thing is, these changes not only improved the sub, but cut costs of construction by a good few million dollars.

An Astute-with-tubes would be an excellent SSGN and potentially a good vector for a cruise missile-based deterrent, at most. 

But the problems connected to a nuclear-tipped cruise missile are numerous and significant:

-        The nuclear-tipped Tomahawk is gone, so there is no easy option.

-        Politically, a new, british development of Tomahawk fitted with a nuclear warhead would be inconceivable. The Tomahawk is one of the most precious, effective and frequently used weapons in the US and UK arsenals, and the political and operational cost of having every single Tomahawk launch possibly mistaken for a nuclear attack is absolutely unacceptable.

-          Developing from scratch a new missile, even one relatively conventional in design, would be expensive, and would also require a new nuclear warhead to be designed. The cost could balloon up immensely if, to counter the greater vulnerability of a cruise missile compared to a ballistic one, the decision was taken to build a stealth and/or hypersonic missile.

-          The cruise missile would never be able to match the useful range of the Trident missile, or its survivability. Shooting down a cruise missile is far easier than trying to kill small warhead re-entering the atmosphere at Mach 25. The range limit means that the current hiding places used by nuclear-armed submarines in the Atlantic and Arctic oceans would be useless: from there, the submarine would be unable to hit anything. What will the submarine do to retaliate against an attack coming from far away, from an unexpected direction, via ballistic missiles? The submarine will run towards a suitable launch area within range of the target, to launch a retaliation days after the attack, risking to be sunk by an enemy which will be aware of the cruise missile threat?   

For a cruise missile to be an effective deterrent capable to hit high-technology enemies (the only ones capable to start an attack requiring nuclear response, arguably), the ability to get past layered air defence systems is indispensable. It should also have thousands of miles of range to enable the submarine to stay a safe distance away from the enemy while it launches the missiles.

And there are only so many routes a low-flying cruise missile can use, making it relatively simply for the enemy to prepare its air defence batteries and, even worse, maritime patrol aircrafts and warships patrolling the possible launch areas.

I think the cruise missile option does not meet the requisites to be considered a Credible deterrent.

Anyway, the Astute-with-tubes solution offers:

-          Negligible savings, assuming that an “hump” solution is adopted to retain Trident missiles. The new submarines will probably cost significantly less, but the design challenge is still significant, and new subs would still be required. Worse still, the new vessels would have their performance depleted or compromised in terms of speed and stealthness. The number of missiles and warheads could shrink further, contributing to the savings, but the reduced number of missiles also reduces the flexibility and lethality of the deterrent. If the firepower shrinks too much and during the life of the deterrent anti-ballistic technology progresses further, an enemy might become realistically certain of its ability to shoot down all the re-entry warheads, nullifying the effect of the deterrent.

-          If the shorter tubes are adopted, and the decision is taken to drop Trident and develop a new ballistic missile, costs rise dramatically. It probably would end up costing more than going onwards with the current plan.

-          If the cruise missile solution is adopted, a new cruise-missile and a new warhead will need to be developed and produced, eroding the possibility of achieving any real saving. All the limits of the cruise missile option will have to be accepted if this road is chosen. 

Flexibility: you can fit a multiple Tomahawk launcher assembly into a Trident tube and still have a lot of space to spare in the bottom half of the tube. Room for future developments and for new uses.

Nuclear-tipped cruise missiles fired from existing, modified Astute subs: the key word here is “modified”. How much modifications will be required to enable the safe carriage of nuclear-tipped cruise missiles in the torpedo magazine? How would said modifications impact the submarine’s performance in its other roles?

This option offers the promise of great savings, even if a new missile and warhead would need to be developed, and the Astute submarines would need modifications for their safe stowage and use. I don’t think, in fact, that it would be accepted to just embark nuclear weapons without proper procedures and equipment being developed.

This option would very likely negatively impact the attack submarine fleet. It would become politically harder to send the Astutes around on their conventional missions, and it wouldn’t be surprising to see nations denying their ports to the visit of an Astute. It could be a real problem in the Persian Gulf.

It is pretty much certain that only one Astute at a time would carry nuclear-tipped missiles, and this one submarine would be hiding like an SSBN, deep into the ocean. It would mean, effectively, dramatically reducing the availability of Astute submarines for their normal missions, and this would have a terribly negative effect on a fleet that is already too small to meet its many commitments. Building at least a couple more Astutes would be absolutely indispensable, but this would further reduce the savings, and there would still be plenty of limits and issues.

Basing the nuclear missiles on surface ships, such as Type 45s, would be even worse, both politically and operationally. And it would also further erode the survivability of the deterrent.

Cruise missiles in a cupboard: this is the most demented proposal after the unrealistic plan for land-based missile silos.

Hiding an entire nuclear arsenal in a bunker in the british countryside will present countless challenges, and I absolutely cannot agree with a course of action of this kind, which would put future british governments in the difficult position of having to order the Navy to open the bunker, load a submarine with missiles and set sail “in times of heightened tension”.

Taking the decision to bring the nukes out of stowage would an hugely impressive move, but it might very easily impress in the wrong way. It could cause a sudden worsening of the situation, instead of bringing back the calm.

There is a big difference between routine patrols going on at sea from well over 40 years and the sudden show of nuclear might connected with the decision to blow the dust off the nukes.

The submarine routinely out at sea is aiming its missiles at everyone, yet at no one at the same time. It is there, somewhere, lurking in the deep, away from the eyes, but always present. It causes prudence, and it cannot be contested.

But the images, shown on television, of long stored nuclear missiles being brought out of the bunker and loaded on the submarine would send a sudden, harsh message which is unlikely to be of real help, because it changes from a routine to an exceptional event, a signal of sudden, dramatic escalation.

Any government would find it hard to take such an important decision.

Worse, this kind of deterrent is not responsive and is not survivable. If, for any reason, the nukes were still in stowage when the first ballistic missile was launched, there wouldn’t be enough time to do anything. The warheads could be raining from the sky in as little as half an hour, and the first nuclear strikes would inexorably target the arsenal.

For me, this option absolutely isn’t credible.

Indeed, in my opinion there is no realistic alternative to a new class of SSBNs. While there are technically different approaches that could be selected, they all ensure a series of problems or degradations in capability, while delivering only rather vague promises of savings.