Dreadnought Class submarines. Crown Copyright MOD

We Give You: Dreadnought Class Trident Nuclear Submarines

Dreadnought Class submarines. Crown Copyright MOD

Somewhere in the world’s oceans, there are always up to four British nuclear submarines patrolling the waters, carrying an arsenal of Trident thermonuclear warheads as part of the UK’s continuous-at-sea-deterrent (CASD) – 24 hours a day, 365 days a year.

The Royal Navy has delivered the nuclear deterrent under Operation Relentless since 1969, with at least one of four nuclear-armed submarines on patrol at all times.

Dreadnought Class submarines will be Britain’s next generation of nuclear deterrent under the Successor programme, replacing the current four Vanguard Class submarines. They are expected to enter service in the 2030s and will be the largest submarines ever operated by the Royal Navy.

Defence, security, and aerospace company BAE Systems is working with partners Rolls-Royce and the Ministry of Defence executive agency, the Submarine Delivery Agency, to design and construct the Deadnought programme to replace Vanguard.

Why Do We Have Nuclear Submarines?

The intention of maintaining an independent centre of nuclear decision making is to make clear to any adversary that the costs of an attack on the UK would outweigh any benefits of such an attack.

The thinking goes that this presence acts as a deterrent because, if, in a worse-case scenario, the nation was targeted by a nuclear attack, and our conventional defence operations were destroyed, the country would still be able to launch a counter strike against an enemy from a remote location beneath the waves, from any quarter of the world, regardless of any damage to the country’s infrastructure.

The philosophy of a nuclear deterrent is based on the theory of Mutually Assured Destruction (MAD) – the principle that if an aggressor knows that by launching a nuclear strike they are also ensuring their own destruction as the other side responds with enough firepower to wipe out a country, then it would be irrational to initiate a nuclear attack in the first place and the simple presence of nuclear warheads is therefore a deterrent to nuclear war.

The submarines that maintain the continuous patrol of the world’s oceans carry warheads that can be launched at different targets.

Government reports suggest that, in spite of the successes of arms control activities in slowing the proliferation of nuclear weapons, the number of states with nuclear capabilities has continued to grow, hence the need to retain a nuclear presence with Trident.


What Is Trident?

Trident is Britain’s nuclear deterrent and while it is a catch-all term to refer to the development, procurement and operation of nuclear weapon defences in the United Kingdom, it more specifically refers to Trident II D5 ballistic missiles that are carried by Britain’s nuclear submarines – currently four Vanguard Class submarines.

The Government says the UK is “committed to maintaining the minimum amount of destructive power needed to deter any aggressor,” adding that “our continuous patrol is essential to assure the invulnerability of the deterrent.”

Our nuclear deterrent is “there to deter the most extreme threats to our national security and way of life, which cannot be done by other means.”

The Government says the UK has reduced its requirement for operationally available warheads from fewer than 160 to no more than 120, meaning the country is now estimated to have a stockpile of 120 active nuclear warheads and 215 warheads in total.

A Government paper last updated in February 2018 says the Government remains committed to reducing the overall nuclear weapon stockpile to no more than 180 warheads by the mid-2020s.

Replacement of the Trident II D5 missile itself is not part of the Dreadnought programme.

The Government has said, however, that the UK is participating in a service-life extension programme for the Trident II D5 missile with the United States, which would extend the life of the Trident missile potentially to the early 2060s.

A judgment on whether to replace Trident, which is expected to retire in the 2030s, will be part of the current National Security Strategy and Strategic Defence and Security Review (SDSR) after the decision was deferred in the 2010 review.

Peacekeeper Missile Launch DoD photo by: STAFF SGT. SCOTT WAGERS

Letter Of Last Resort

Every nuclear submarine fitted with thermonuclear warheads carries a sealed ‘Letter Of Last Resort’ – a handwritten letter from the Prime Minister to each submarine’s commanding officer.

It contains instructions on what action the vessel's commander should take in the event that Britain is obliterated by nuclear attack and all those in authority deceased, the government annihilated.

The letter is understood to contain four options: retaliate, don't retaliate, use your own judgement (the commanding officer’s judgement), or place command of the submarine under US or Australian command if possible and necessary.

Advantages Of Nuclear Submarines?

Nuclear-powered engines provide a wealth of advantages over a standard submarine, such as one with a traditional design and a diesel-powered engine for instance, that go beyond the longevity of nuclear power.

A small amount of basic fuel produces large volumes of energy meaning nuclear submarines do not need to be refuelled for more than 20 years.

However, there are other strategic advantages of these submarines.

Nuclear engines are substantially quieter than conventional combustion engines – a vital requirement of stealth defence.

They also do not need to resurface on a frequent basis – with the next generation of Dreadnought submarines able to generate their own oxygen and fresh water, meaning they can stay deep in the water for months at a time.

The classification SSBN is hull classification symbol for a nuclear-powered, ballistic missile-carrying submarine in which the SS denotes submarine (or submersible ship), the B denotes ballistic missile and the N denotes that the submarine is nuclear powered.

Ministry of Defence Dreadnought Crown Copyright

Dreadnought Submarines – All The Gen

More than simply a replacement for the Vanguard-class, which are Britain’s current fleet of nuclear-powered ballistic missile submarines, the Dreadnought is also a new design that takes advantage of technological advances and new production methods to meet the changing threats to the UK’s defence and security.

Specific details of Dreadnought, like all nuclear submarines, are of course classified, with the most sensitive of information withheld from the public in the interests of national security.

Here, however, we take a look at what can be revealed about the next generation nuclear submarines that deliver Britain’s Trident nuclear deterrent operating systems.

What Is The Dreadnought Programme?

The programme is often referred to as the renewal or replacement of Trident – but the programme is specifically focussed on the design, development and manufacture of four new Dreadnought Class ballistic missile submarines (SSBN), as the Vanguard submarines progress to the end of their lifespan.

It was initiated after Parliament voted in 2016 to renew Britain’s continuous at sea deterrent, at a cost of £31 billion – while sustaining the nuclear deterrent in-service is expected to account for about 6% of the annual defence budget.

The Dreadnought programme employs more than 7,000 people across the Ministry Of Defence and industry, including 2,800 at BAE Systems.

BAE says that thousands more will be employed in the supply chain.

A Common Missile Compartment (CMC) for the SSBN, which will house the existing Trident strategic weapons system, is being developed in conjunction with the United States.

The Dreadnought Class submarine is expected to have a service life of at least 30 years once it enters service in the early 2030s.

Contracts were signed by the Ministry of Defence in May 2018 which set in motion the design and build of the first Dreadnought submarine, with a second submarine underway.

The contract also includes the design and manufacture of the nuclear propulsion power plant.

A report in 2019 by the MOD revealed that the programme remained on schedule.

Royal Navy Vanguard Class submarine
A Royal Navy Vanguard Class submarine. Crown Copyright.

What Is The Difference Between Vanguard And Dreadnought Class Submarines?

From the limited information available that is not understandably classified, there are notable subtle but significant differences between the Vanguard and Dreadnought Class submarines.

The differences are thought to be the result of improved efficiencies, improved technology, reduction in costs and adherence to new treaties on denuclearisation such as the New Start (Strategic Arms Reduction Treaty), a treaty between the United States and the Russian Federation which agrees to reduce the number of strategic nuclear missile launchers. It follows a previous Start treaty that limits the deployment of nuclear warheads.

Key Differences

One of the most striking differences is that the Dreadnought Class is expected to have fewer missile tubes than the Vanguard – 12 instead of the current 16, each carrying up to eight Trident II D5 nuclear ballistic missiles.

There is likely to be various reasons for the change – again down to technological advances in design, more facilities for crew and other design considerations such as a larger reactor, but the designers will perhaps be closely monitoring the thinking around the future of Trident and how this might affect the overall construction.

The House of Commons Library, an independent research and information service based in the UK Parliament, reports that questions continue to be asked about the rationale for the deterrent and whether its replacement contravenes the UK’s international legal obligations, adding:

“The next major decision is whether to replace the current nuclear warhead, which is expected to retire in the late 2030s. To meet that deadline a decision needs to be taken in this Parliament.”

In May 2019, the then Defence Secretary Penny Mordaunt, in a written answer to Parliament, said that work was continuing to refine options and technical solutions to inform the Government's decision on replacing the warhead.

This will perhaps be a consideration that might influence the development of the Dreadnought and its variation from the Vanguard Class.

HMS Vanguard's DASO Trident missile test
HMS Vanguard's Trident missile test launch. Crown Copyright.

Future Of Trident

These questions over the future of the warhead have led to speculation that the Dreadnought could be reconfigurable to carry TLAM, the Tomahawk Land Attack Missile, a missile system initially developed in the 1970s by defence corporation General Dynamics, but there is little information to support such conjecture.

A TLAM operation is perhaps unlikely in any commitment to a continuous at sea deterrent in which positioning in deep undetectable water is paramount as opposed to shallow inshore waters in a conventional TLAM launch.

Another key difference between the Dreadnought and the Vanguard is that the Dreadnought will be the first Royal Navy submarine fitted with aft X planes in a combined hydroplane and rudder, instead of the standard rudder and planes formation.

The design of the Dreadnought also brings them in a three-metres longer than the Vanguard Class, while the Dreadnought’s displacement is about eight per cent over the Vanguard’s at 17,200 tonnes.

While specific details of size differences will again be subject to secrecy, the differences from the Vanguard are likely to be influenced by the need to accommodate a new technologically-advanced PWR3 reactor and improved crew facilities, including a design spec to accommodate female crew members, as the Dreadnought will be the first Royal Navy submarine to be fitted with separate female crew quarters, toilets and washing facilities.

Other design differences are expected to be influenced by more efficient acoustic quieting techniques and the variation in size from the Vanguard perhaps reflects new technologies to accommodate this.

Other improvements include a state-of-the-art medical centre, a gym, education facilities and study area as well as a new lighting system that will simulate day and night, no doubt to improve wellbeing among the crew.

As the Dreadnought incorporates a raft of new technology, an up-to-date system to operate the entire vessel is also needed, and this comes in the form of an integrated platform management system – a type of central digital software control centre which controls and monitors the submarine's platform machinery and onboard systems, incorporating propulsion, electrical systems and damage control in one integrated platform.

The Dreadnought submarines will be named HMS King George VI, HMS Dreadnought, HMS Valiant and HMS Warspite.


Picture: BAE Systems

Dimensions Of The Dreadnought:


153.6 metres long – about the length of 13 London buses.


17,200 tonnes


The Dreadnought class submarines will have their own classroom and study area set aside in a first for a Royal Navy submarine.


A Royal Navy doctor will have a designated ‘sick bay’ to carry out routine check-ups, make diagnoses and dispense medicines.

The facility is also designed to be able to care for a major casualty if an incident necessitates as such.


The submarines’ crew will be able to maintain their Royal Navy fitness standards by working out in a fully-equipped gym, complete with exercise bikes, rowers, weights benches, a running machines and a cross trainer.


Dreadnought submarines have been designed for 130 crew members. The contingent will include three chefs and one Royal Navy medic.

Female Crew:

The Dreadbought class will be the first Royal Navy submarine to be fitted with separate female crew quarters, toilets and washing facilities.


The Dreadbought class has 42.5 km of piping.

That's enough to stretch almost to Chelmsford in Essex from London’s Trafalgar Square.


More than 20,000 cables linking the submarines’ electrics will be installed into the design – enough to stretch 347km, about the distance from London’s Trafalgar Square to Paris in France.


There will be almost 13,000 electrical items on board the submarines.


An innovative new lighting system on board the Dreadnought class will allow the crew to simulate night and day in a first for a Royal Navy submarine.


The Dreadnought class will manufacture its own oxygen and fresh water as it provides a continuous at sea deterrence in defence of the United Kingdom.

BAE Barrow-in-Furness Shipyard BAE Systems picture
BAE’s Submarines site at Barrow-in-Furness. Picture: BAE Systems.


BAE Systems says that the whole Dreadnought programme already employs more than 7,000 people across the Ministry of Defence and defence industry. This includes about 2,800 at BAE Systems.

The defence business says that thousands more will be employed in the supply chain during the course of the programme.


BAE’s Submarines site at Barrow-in-Furness has been undergoing a redevelopment with more than £300m investment in readiness to accommodate the build of Dreadnought and maintain its “proud history of delivering complex submarine programmes.”

Some 24 separate projects are involved in the redevelopment, which the business says marks the largest investment in the site since the Devonshire Dock Hall was constructed in the 1980s.

Fragment fuel uranium rod element of nuclear reactor. By Parilov/Shutterstock
Fragment fuel uranium rod element of nuclear reactor. By Parilov/Shutterstock.


A PWR3 nuclear reactor, turbo-electric drive, pump-jet propulsion system from Rolls-Royce.

Naturally, a level of defence operational secrecy is maintained regarding the intricate specifications of military systems and nuclear reactor designs while operating methods and performance standards are highly classified.

However, the PWR3 follows two earlier models – the PWR1 and PWR2 – and the PWR3 is a new system that is based on a US design but incorporating UK reactor technology.

To give an idea of how the operations of a standard nuclear industry pressurised water reactor work, they essentially generate steam to drive a turbine to produce electricity and power, with a basic nuclear fuel generating the power.

Basic Fuel:


Nuclear industry PWRs, such as those found in a power plant, have fuel assemblies of about 200 to 300 rods, arranged in a core while larger reactors would have up to 250 fuel assemblies – powered by up to 100 tonnes of uranium.

Rolls-Royce says that only a “small spoonful” of uranium in the PWR3 is all it takes to power a fully-submerged submarine on a full circumnavigation of the world’s oceans.

A basic description of how such nuclear reactors might operate, in, say, a power plant environment, is by using ordinary water to generate pressure through steam, with water in a reactor core reaching above 300°C.

Overheating at such high temperatures is kept under control through pressure – more than a 100 times normal atmospheric pressure - to prevent boiling temperatures spiralling upwards.

The pressure is kept in check by pressurised steam, with a primary cooling circuit using water as a moderator as well as coolant – and steam slowing down the fission reaction, providing a safety feature.

A secondary shutdown system would see the chemical element boron, a non-metallic substance often found in glass or detergents, flushed into the primary circuit. Borated water used as a coolant can quickly remove heat from a nuclear reactor core and transfer heat to a secondary circuit, with the reactivity of the reactor rapidly adjusted by changing the boron concentrations.

The distinguishing features of PWR design is a primary cooling circuit which flows through the core of the reactor at high pressure, and a secondary circuit that generates steam to drive the turbine.

Its manufacturers say the PWR3 reactor that will power the Dreadnoughts is a brand new design and is not just an evolution of the PWR2 used on the Vanguard and Astute class.

They say it will meet higher safety standards and be easier to maintain while being more cost-efficient, with a simpler design that requires fewer coolant pumps, making it significantly quieter.

Reactor Core Lifespan:

Rolls Royce says that a single core reactor could last longer than 20 years.

Spearfish Torpedo
An artist's impression of the Spearfish Torpedo design



Dreadnaught Class submarines are expected to be armed with four 21in torpedo tubes which will house Spearfish torpedoes by BAE Systems.

Spearfish Torpedo:

By far the fastest torpedo in the NATO alliance, the Spearfish is driven by a gas turbine engine driving a pump jet and, following a £270m MOD contract to upgrade these munitions in a deal with BAE Systems, the torpedoes will come equipped with new warheads, an improved fuel system, and digital technology and fibre optic guidance links.

Spearfish torpedoes travel at a speed of up to 80 knots (about 148kph) – over and above the speed of other standard torpedoes such as the American MK 48, which run at about 30 knots (50kph).

Nuclear Deterrent:

The submarines are designed to carry thermonuclear warheads which will feature as part of its Trident II D5 missile system.

Dreadnaught’s 12 ballistic missile tubes will be capable of firing up to 12 Lockheed Trident II D-5 ballistic missiles.

The Trident II D5, the latest generation of submarine-launched ballistic missiles as used by the US Navy, can carry eight warheads each.


Dreadnaught Class is expected to be fitted with type Sonar 2076, developed for the Royal Navy by the Thales defence group.

Thales Underwater Systems says its type Sonar 2076 is the world’s most advanced, fully integrated, passive / active search and attack sonar suite.

It is a system that has also been fitted in both the Trafalgar Class and Astute Class submarines.

This sonar capability comes with mine detection and UHF intercept arrays.


Defence firm Thales UK has also been awarded a £330 million contract to work on periscopes and other underwater systems for the Royal Navy’s next generation Dreadnaught Class nuclear submarines.

Technology on the masts will include a visual and situational awareness sensor, as well as a sonar system and electronic warfare technology and cameras that will provide a "visual link" to submariners, according to the Ministry of Defence.

Modern-day periscopes are able to sense threats from the sea and sky.

Working alongside ground-breaking threat-detection technology, platform management system, and sonar, it will enable the Dreadnought to sense threats from aircraft or other naval vessels without having to surface. 

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