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Successor Submarine

(also known as the Future Submarine (FSM))

Type Designation: SSBN


(Above) HMS Vanguard, she is due to be replaced around 2028.   (Source: Ministry of Defence)


(Above) It is possible that the Vanguard replacement will be a much evolved variant of the Astute class, with a ballistic missile tubes inserted aft of the sail. (Source: BAE Systems)


(Above) A model of a possible evolved version of the Vanguard class ballistic missile submarine, developed by BAE Systems Submarine Solutions as 'Concept 35'. (Source: Aviation Week)


Boat Pennant Number Commissioned Expected Builder
B-01 S? [2028?] BAE Submarines Solutions, Barrow
B-02 S? [2030?] BAE Submarines
B-03 S? [2032?] BAE Submarines
B-04 (Requirement to be confirmed) S? [2034?] BAE Submarines


Displacement: ?
Dimensions: ?
Speed: ?
Engines: ?
Missiles: Trident II D5
Torpedoes: ?
Complement: ?


Project designation: URD ?
Status: Passed Initial Gate and entered Assessment Phase in May 2011.   Main Gate is officially expected 2015
In Service Date:  By 2028

The Trident II D5 missile system eventually entered UK service in 1994, and is deployed on a force of four specially built nuclear-powered ballistic missile submarines (SSBN’s) – HMS Vanguard, Victorious, Vigilant and Vengeance, based at Faslane.  On 4 December 2006, the government announced the decision in principle to maintain the UK's independent nuclear deterrent beyond the 2020's and replace the existing submarines with a new class of three or maybe four SSBN's, a vote in parliament support this decision and made the project all but certain to proceed .



Government ministers have implied that low key “routine … studies in to options” for replacing Trident have in fact been in progress since at least 2002.

In August 2003 it was ten years since the lead boat, HMS Vanguard, commissioned - her first deterrent patrol was in begun in December 1994.  In 2005 she returned to service after  completing at DML Devonport the first of the two Long Overhaul Periods (the first including a nuclear refuelling) planned during her service life.  She was designed with a twenty-five year hull life and thus was expected to require replacement by about 2019, but a less demanding operational profile and deployment cycle than originally anticipated will allow her projected service life to be extended to 2024 if required.  Nevertheless, experience has shown that a near twenty year lead time is needed for any replacement system

In the Defence White Paper Delivering Security in a Changing World ( Cm 6041) published in December 2003, it was stated that: “Decisions on whether to replace Trident are not needed this Parliament but are likely to be required in the next one.”   That Parliament  ended in May 2005. 

In May 2004 the First Sea Lord, Admiral Alan West, told a conference held by Royal United Services Institute that a Trident replacement decision was expected within the next two to three years.

Press reports indicated that in May 2005 the Prime Minister, Tony Blair, had authorised further studies.  In May 2005 Tony Blair said during a BBC interview "We've got to retain our nuclear deterrent, and we've had an independent nuclear deterrent for a long time. Now that decision is for another time, but in principle, I believe it's important to retain our own independent deterrent. I believe that is the right thing for the country, I think it's important that however we look at all the different aspects of it. Any decision hasn't yet been taken"  

On the 4th July 2005 the Secretary of State for Defence, John Reid, echoed this view when he told the House of Commons  “Decisions on any replacement of the United Kingdom’s nuclear deterrent are likely to be necessary in the lifetime of the current parliament, which will of course last some years.”

A driver supporting this timetable an increasingly urgent need for BAE Submarines (and perhaps BMT and QinetiQ) to have a [real] Astute follow on project in order to maintain an expensively and painfully redeveloped national nuclear submarine platform design and engineering capability, and also to assure UK suppliers that there is a long term future in a very specialist sector.   Any further erosion of the industrial base  would be disastrous as most systems and services are now already only available from a single source - and some companies faced with the reality of losses so far on Astute work are wavering.  The MOD and DPA also wants to use the prospect of new orders to encourage consolidation and rationalistion (e.g. the formation of a single Submarine platform and propulsion company  - SubCo) in order to reduce the cost base and improve efficiency. 

On 4 December 2006 the government indicated a decision to maintain the UK's nuclear deterrent, building a class of 3 or 4 SSBN's to replace the Vanguards from 2004.

On the 4th December 2006 the MOD released the Defence White Paper "The Future of the United Kingdom’s Nuclear Deterrent".

Ina  statement to Parliament Prime Minister Tony Blair has told MPs it would be "unwise and dangerous" for the UK to give up its nuclear weapons.

"The current Vanguard submarines have a service life of 25 years. The first boat should leave service in 2017. We can extend that for five years. In 2022, that extension will be concluded and in 2024 the second boat will also end its extended service life.

By this time, we will only have two Vanguard submarines. This will be insufficient to guarantee continuous patrolling.

The best evidence we have is that it will take us 17 years to design, build and deploy a new submarine. Working back from 2024, that means we have to take this decision in 2007. Of course, all these timelines are estimates, but they conform to the experience of other countries with submarine deterrents as well as our own.

Secondly, we have looked carefully at the scope of different options. The White Paper sets them out. Aircraft with cruise missiles - but cruise missiles travel at subsonic speeds and building the special aircraft would be hugely expensive. A surface ship equipped with Trident - but a far easier target. A land-based system with Trident - but in a small country like the United Kingdom immensely problematic and also again an easier target. There is no real doubt on this score: if you want an independent nuclear deterrent, for a nation like the UK, a submarine-based one is best.


A new generation of submarines will make maximum use of existing infrastructure and technology. The overall design and manufacture costs - of 15-20 billions - are spread over three decades; are on average 3 per cent of the defence budget; and are at their highest in the early 2020s. As before, we will ensure that the investment required will not be at the expense of the conventional capabilities our armed forces need. It is our intention that the procurement and building will, as now, be done by British industry, with thousands of British, highly-skilled jobs involved.

However, we will investigate whether, with a new design, we can maintain continuous patrol with a fleet of only three submarines. A decision on this will be made once we know more about the submarines' detailed design. No decisions are needed now on the warhead. We can extend the life of the D5 Trident missile to 2042. After that, there will be the opportunity for us to participate in any new missile design in collaboration with the US, something which will be confirmed in an exchange of letters between myself and the President of the USA.

Maintaining our nuclear deterrent capability is also fully consistent with all our international obligations. We have the smallest stockpile of nuclear warheads amongst the recognised nuclear weapons states, and are the only one to have reduced to a single deterrent system. Furthermore, we have decided, on expert advice, that we can reduce our stockpile of operationally available warheads to no more than 160, which represents a further 20 per cent reduction. Compared with previous plans, we will have reduced the number of such weapons by nearly half. "

After extensive public debate, a Parliamentary vote on 14 March 2007 supported the replacement of Trident. and a final decision by the government to initiate the project was expected within months.

Current Situation

In May 2007 the MOD's Defence Equipment and Support organisation (DE&S) stood up the Future Submarines (FSM) Integrated Project Team (IPT) to co-ordinate the project work. 

One of the teams initial priorities has been initiating studies to determine whether three or four new submarines will be required.  Three submarines  would seem to be a highly risky strategy - experience with  Resolution class SSBN's showed the significant fall off in operational availability that occurs as submarines age.  Three young submarines would allow a continuous deterrent patrol - but only as long as no accidents occurred while one was in a overhaul period.  However it seems very unlikely that this would still be possible as they reached 20+ years of age - at least  without significant technological breakthroughs, and/or an extraordinary level of redundancy in the design.  There is is high probably that a three boat class designed and built to meet extremely demanding availability and serviceability requirement will cost very little less than four boats built to more main stream standards - whilst having a much higher level of risk of gapping Britain's nuclear deterrent.

On 18 October 2007, a press release by BAE Systems stated:

 "Today ... Rear Admiral Paul Thomas CB, FREng chairman of the defence nuclear safety committee, officially opened the Future Submarines (FSM) Integrated Project Team office at Barrow-in-Furness.

This element of the Future Submarines IPT will be based on the BAE Systems Submarine Solutions site and will be manned by a collaboration of up to 128 personnel made up from the Ministry of Defence, BAE Systems, Rolls Royce and Babcock Marine. Working with the FSM IPT office in the MoD’s Abbey Wood offices, the team will, over the next two years, develop a concept design for the submarine component of the future deterrent programme.

The future deterrent programme is one of the most significant programmes to be defined, managed and delivered by the UK defence community over the next two decades, and has potential to shape the submarine industry for years to come. The IPT will work closely with external stakeholders in industry to develop and deliver an affordable, sustainable and coherent programme with an associated management framework.

The integrated team is led by Andy Mackinder from the MOD, who said, “This is an exciting day for everyone involved in the future deterrent programme My team has started design concept work on a new class of SSBNs to replace the current Vanguard Class. This office is a significant part of our plans for delivery of this strategically important programme.”

Tony Burbridge from BAE Systems is the deputy IPT leader and industrial partnership leader."

The FSM IPT is now engaged in a two-year programme of concept work, with representatives from the Ministry of Defence (MoD), BAE Systems, Babcock Marine and Rolls-Royce.  The concept phase activities have been split into two parts, the first is concentrating on what form the major system functions will take, including propulsion, combat systems, and strategic weapon systems.

Informed by these outputs and their attendant option sets, a second phase of concept work will develop a coherent and costed submarine design that will meet the overall requirement as well as meet affordability criteria (both in terms of unit production cost and whole-life cost).  The FSM programme is expected to reach the Initial Gate milestone in the second half of 2009.

Other major systems decisions and Main Gate approval should follow on. Current plans are for a seven-year design phase, a seven-year build phase and a period of sea trials before the first boat enters service.

While a parliamentary vote on 14 March 2007 endorsed the current governments (Labour Party) plans to renew the UK's Trident deterrent, it remains uncertain that the new generation of SSBNs will actually be built - this and the commitment of most of the associated £15-20 billion will be a decision for a future government to make between 2012 and at the latest 2014.  If the project is cancelled at that stage, the write-off in expenditure is expected to be about £1 billion.



Trident II D5 launch

The government identified a number of options for future of the UK's strategic nuclear deterrent, in approximate order of increasing cost these were:

  • Don't replace Trident - leaving France as the only EU member with nuclear weapons;
  • A small force of vulnerable land based ballistic missiles.
  • Ship based ballistic missiles - probably initially Trident.
  • Build a new class of SSBN's, initially carrying extended life Trident missiles or a replacement submarine ballistic missile system.
  • Develop a cruise missile with a nuclear warhead, air launched by a force of 20 RAF strike aircraft supported by 20 dedicated refuelling aircraft.

A submarine based solution was announced as the preferred choice in December 2006.  Initial government estimates were that the programme would cost about £20 billion, perhaps about £9 billion of which (in current money) is for the replacement of the replacing the four Vanguard’s with another  class of 16 tube ballistic missile submarines.  If this money was taken solely from the RN's current share of the MOD's equipment budget then no other new ships or submarines could be ordered for the RN for a period of at least 15 years.


SLEP'ing the Vanguard's

In addition to new build, MOD officials investigated the costs involved with a service life extension programme (SLEP) for the four existing Vanguard class submarines, and their Trident missiles, re-entry vehicles and W-76 derivative nuclear warheads.  Since 2006 the government and MOD have apparently assumed as a near given a 5 year extension in the V's service life, from 25 to 30 years.

Developments in the USA (see below) indicates that it might be possible for the UK to economically extend the system to serve for yet another 10-15 years - but this would be very costly.  At the very least the boats would unexpectedly need another expensive long overhaul period and refuelling (LOP(R)), and their hulls and nuclear steam plant would need to be critically inspected and recertified.  Some UK experts (e.g. Commodore Tim Hare RN (Rtd)) believe that the Vanguard's are being too hard worked for a full SLEP (extending their service life by 20 years) to be possible, rather than the 5 year life extension widely discussed.  it's also worth noting that SLEP'ing the V's would almost inevitably result in the loss of a national nuclear submarine construction capability, and this will have to be factored in. 

Across the Atlantic, the US Department of Defense is pressing ahead with a Trident II D-5 life extension (LE) program, the first contracts for which were awarded in 2002.  The USN now expects to operate the Trident II D5 missile from SLEP'ed Ohio class submarines until about 2042.  Also, on 26 May 2005 the US Department of Defense announced the award to Lockheed Martin a $9 million contract in regards to development of an affordable Submarine Launched Intermediate Range Ballistic Missile (SLIRBM). The SLIRBM will have a maximum diameter of 32.5 inches, less than half the diameter of a Trident II, but a range not exceeding 2000 nm, again less than half that of a Trident II. The missile could accommodate both nuclear and non-nuclear GPS guided warheads.  Allegedly, UK MOD officials have already been involved in discussions about the project.


The Expected Life of the Trident System

(Source: House of Commons Defence Committee Publications , January 2006)

1. The UK's current nuclear deterrent capability comprises several elements: first, the nuclear warheads, which were designed and manufactured in the UK by the Atomic Weapons Establishment; second, the Trident D5 missiles, which were procured from the United States under the Polaris Sales Agreement (as amended for Trident); third, four Vanguard-class nuclear powered submarines, built at Barrow-in-Furness by what was then Vickers Shipbuilding and Engineering Limited, who also designed the bulk of the submarine; and finally a range of logistic infrastructure - at the naval facilities at Coulport (weapons handling and storage), Faslane (submarine basing) and Devonport (submarine refit and maintenance).

2. While each element of the capability has a design life, its longevity in practice is not fixed, as items can be withdrawn from service before the end of their design life or, alternatively, the design life may be extended by updates, refurbishments or by being able to run on a system for longer, based on experience gained during its operational life. The current situation is as follows:

a) The Warhead:

The current warhead came into service with the Trident system in 1994. An extensive research programme to assure the safety and effectiveness of the warhead stockpile, coupled with the additional investment at AWE Aldermaston announced on 19 July 2005, gives a high level of confidence that the current warhead design can, if required, be maintained in service at least into the 2020s, with some relatively minor upgrading and refurbishment during the first half of the next decade .

b) The Ballistic Missiles:

The Trident D5 missile came into service with the Royal Navy in 1994, with a planned life of some 25 years. The US Navy has recently announced plans for a life extension programme for the D5 missile, which will ensure it can remain in-service with the US Navy into the 2040s. The UK Government has yet to decide whether or not to participate in this programme.

c) The Submarines:

HMS VANGUARD entered operational service with the Royal Navy in 1994, with the other three submarines in its class following in 1995, 1998 and 2001. The submarines were procured with a designed operational life of 25 years and on this basis, they would start to be withdrawn from service late in the next decade. A series of studies have considered whether it would be practicable and cost effective to continue to operate the submarines beyond the original design intent. We now believe that, if required, this would be possible, albeit with gradually increasing cost and some increasing risk of reduced availability, perhaps out to the mid-2020s.

d) Shore Infrastructure:

Under the Trident programme, successive Governments have made significant investment in the facilities at Coulport, Faslane and Devonport. We envisage that the facilities at these locations needed to support the nuclear deterrent will not require any significant additional investment to sustain them throughout the currently planned in-service life of the existing system. Clearly, the extent of any additional investment in logistics or infrastructure beyond that point will depend on future decisions on whether and how to maintain a nuclear deterrent beyond the planned life of the current system.


New build

New build submarines is now the favoured option to replacement the Vanguards. 

The Astute project currently seems likely to end with the completion and delivery of the seventh boat around 2019, and conveniently the first Vanguard replacement is required in 2021.  Bitter experience with the Astute project shows that for industrial continuity design work on any new class (or major variant) must start by 2007 (Initial Gate), with steel being cut in 2015, with Prime Minister Blair stating in March 2007 that Main Gate approval would need to occur between 2012 and 2014.

In order to keep costs down, an all-new submarine design has become considered unlikely for a Vanguard-class replacement and current thinking probably assumes an evolution of the Astute design - indeed BAE Systems Submarines has already examined two variants fitted with an extra hull section. The first includes the fitting external to the pressure hull of sixteen Mark 36 Vertical Launch System tubes for missiles such as Tomahawk, and the second includes four Trident II size (86 inch diameter, 36-feet usable length) missile tubes, installed aft of the fin.  The later approach is preferred as the large tubes are extremely versatile, alternative to Trident II SLBM’s they could potentially carry a next generation ballistic missile, a multiple all-up round canister accommodating seven Tomahawk cruise missiles per tube, equipment and swimmer vehicles for special forces, Unmanned Underwater Vehicle’s (UUV’s), deployable decoys and sensors, and even encapsulated Unmanned Air Vehicle’s (UAV’s).  While a re-role will not be trivial, the new submarines would certainly be far more flexible than the current SSBN/SSN divide permits.

While utilising a modified Astute design to carry Trident has been much discussed for several years, officials are now (December 2006) making it clear that this is not a trivial exercise, at the very least a major and costly redesign will be required.  The final result may have as much similarity to the Astute's as the Astute's (originally called Batch 2 Trafalgar's!) have to the T's and V's.

The service entry date for the first Vanguard replacement is still far from certain.  At the latest it would be timed to allow replacement of HMS Vanguard by 2024-25, but with an Astute derivative approach a much earlier date would be technically possible.


BAE Submarine Concepts

At DSEi in September 2007, BAE Submarine Solutions unveiled some of its thinking that it and industry partners were developing to inform the the MOD's Future Submarine project.  In particular they displayed  two concepts.

Concept 35 was a relatively conservative approach clearly evolved from the Vanguard class, it was developed primarily to illustrate a submarine design philosophy ultimately driven to reduce costs throughout the whole life of the submarine - which had become a major influence driving the redesign of the Astute-class.  The philosophy included:

  • Simplifying submarine assembly
  • Removing the need for extensive and intrusive dockyard modernisation
  • Reducing the number of piece parts and bespoke submarine systems
  • Doing nothing that would impact adversely on the submarine signature or safe operation

Concept 35 demonstrated how technology can deliver this substantial and sustained reduction in cost of ownership of submarines.   The concept also included:

  • A next generation Naval Propulsion Plant, with extensive passive features and designed for disposal
  • Extensive use of automation for submarine control, damage control and condition monitoring
  • Full electric propulsion with shaftless drive
  • Externally mounted tactical weapons
  • Electrical actuation of control surfaces
  • Replacement of obsolescence equipment, with extensive use of current military and commercial off-the-shelf equipment.

(Above) A model of BAE's Advanced Hull Form submarine concept. (Source: D McArthur

Rather more ambitious was the Advanced Hull Form submarine concept, this uses modular design techniques and advanced hydrodynamic thinking to break out of the constraints imposed by the classical body of revolution design.

The resulting unusual external hull form offers advantages in signatures, manoeuvring and safety, and provides large volumes for payloads and equipment outside the pressure hull. This gives exceptional flexibility in design and operation, with the maximum opportunity for rapid role change or upgrading.

Safety is enhanced by the hydrodynamic design, which offers improved manoeuvring and emergency recovery compared with current designs. It is further improved through the external payload and equipment locations, which minimise hull penetrations and improve watertight integrity.

The Advanced Hull Form has been designed for low cost fabrication using largely flat or single curvature surfaces. This approach also allows rapid repair and modification, giving the basis for a flexible and economical platform through life.


Vanguard Replacement Links

Note: Links open in new windows

House of Commons Defence Committee - The Future of the UK’s Strategic Nuclear Deterrent: the Strategic Context, Eighth Report of Session 2005–06

House of Commons Defence Committee - The Future of the UK’s Strategic Nuclear Deterrent: the Strategic Context, Written evidence from the Ministry of Defence

The Future of the United Kingdom’s Nuclear Deterrent: Defence White Paper 2006 (Cm 6994)

See also: MUFC



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 © 2004-13 Richard Beedall unless otherwise indicated.