Upgrading the Royal Navy’s Nuclear Submarine Support Facilities

 In Sea, Forces & Capabilities, Nuclear Reactors, Materials, and Waste

Plans to con­vert anoth­er dry dock in Devonport to refit the Dreadnought class sub­marines were recent­ly revealed in an out­line plan­ning appli­ca­tion. Here we exam­ine the con­text and rea­sons for the upgrade.

Number 10 Dock is the biggest dry dock at Devonport and Babcock Marine, who oper­ate the yard, have plans for a com­plete refur­bish­ment to create a second facil­i­ty cer­ti­fied to take the largest nuclear sub­marines. Stringent modern reg­u­la­tions require that the nuclear facil­i­ties must have redun­dant sys­tems and be able to with­stand earth­quakes, high tides and high winds. The require­ment to with­stand a severe earth­quake (Considered likely to happen, just once in 10,000 years in Plymouth) is par­tic­u­lar­ly demand­ing from an engi­neer­ing per­spec­tive. Very robust struc­tures are needed and sys­tems such as cool­ing water and elec­tri­cal power need to have mul­ti­ple back­ups in the event of fail­ure.

Between 1999 and 2002 the adja­cent number 9 Dock was refur­bished to con­duct refits and refu­elling of the Vanguard-class sub­marines. The orig­i­nal dock floor was removed and a new floor with inte­gral drainage system was con­struct­ed and fitted with a cradle to secure the sub­ma­rine. The old dock was con­sid­er­ably nar­rowed by lining with coun­ter­fort walls con­struct­ed on top of the new dock floor. A new dock­side edge struc­ture (cope) with ser­vice sub­ways to carry piping and cables was con­struct­ed on top of the coun­ter­forts. The cope was secured by more than sev­en­ty, 760-mil­lime­tre diam­e­ter steel piles anchored in 12-metre sock­ets anchored in the rock. The dock entrance is sealed by very large multi-cel­lu­lar cais­sons and seis­mi­cal­ly-qual­i­fied dock­side cranes have been installed.

To enable nuclear refu­elling, a new Reactor Access House (RAH) was built that moves on rails to be aligned over the reac­tor com­part­ment. Spent fuel can be raised up into the RAH and new fuel rods low­ered into place. At the head of the dock, a Primary Circuit Decontamination and Alternative Core Removal Cooling (PCD/ACRC) system build­ing was con­struct­ed. The PCD/ACRC build­ing con­tains the plant used to cool the reac­tor, apply chem­i­cal decon­t­a­m­i­na­tion and inject or remove boronat­ed water reac­tiv­i­ty sup­pres­sant. The building’s equip­ment and plant is con­nect­ed by over 20 km of pipework and 150 km of elec­tri­cal cable in 92 rooms.

CGI showing preliminary design proposal for the refurbishment of 10 Dock and the new support building to be constructed on the west side. (Image: Arcadis Consulting UK )

The new devel­op­ment at 10 Dock will have sim­i­lar­i­ties with the 9 Dock upgrade project but does not have the cost of com­plex­i­ty of the RAH and PCD/ACRC as it is not intend­ed to be used for nuclear refu­elling or de-refu­elling oper­a­tions. The 2.61-hectare dock will be con­sid­er­ably nar­rowed and short­ened by the rein­force­ment of the East and West walls and con­struc­tion of a new head­wall (the white areas on the mockup). The dock will be served by elec­tri­cal, water and waste pipework accom­mo­dat­ed in subway struc­tures in the new walls. A new Water Retaining Boundary (WRB) will be built to pro­tect the dock from tidal surges and pos­si­ble future water level rise asso­ci­at­ed with cli­mate change. Two obso­lete sup­port build­ings, N125 and N093 on the west side of the dock will be demol­ished and replaced with a single build­ing con­tain­ing offices, pro­duc­tion facil­i­ties and staff ameni­ties.

The phased project is planned to begin in 2021 and Babcock esti­mates the peak con­struc­tion time is likely to be between late 2022 and early 2025. New jobs will be cre­at­ed and up to 650 work­ers will be employed on site. It should be noted that the design is still under devel­op­ment and may be refined fur­ther, the pro­pos­als made public so far are for the pur­pos­es of envi­ron­men­tal assess­ment.


9 and 10 Dock was were con­struct­ed between 1896 and 1907 to accom­mo­date the rev­o­lu­tion­ary new class of Dreadnought bat­tle­ships. As bat­tle­ships rapid­ly devel­oped, acquir­ing heav­ier guns and armour they grew in dis­place­ment, con­sid­er­ably beyond what the archi­tects of the dry docks had orig­i­nal­ly envis­aged. The 38,000-ton bat­tle­ships Nelson and Rodney, built during the 1920s, had a beam of over 32 meters, wider than any pre­vi­ous cap­i­tal ships. Between 1936 – 39, Number 10 Dock at Devonport was been enlarged and could accom­mo­date any ship in the navy, except HMS Hood.

10 Dock con­tin­ued to be used for dry-dock­ing the RN’s largest ships into the modern era, most recent­ly the refit of HMS Albion com­plet­ed between 2014 – 17. With the loss of HMS Ocean, the LPDs are the only large cap­i­tal ships left (apart from the QEC car­ri­ers that are too large for any of the dry docks in Portsmouth or Devonport). Assuming HMS Bulwark is even­tu­al­ly re-acti­vat­ed, she can be accom­mo­dat­ed in the slight­ly small­er number 8 Dock, which will be the last remain­ing big dry dock at Devonport. The other large ves­sels of the Naval Service belong­ing to the RFA are main­tained away from the naval bases, at facil­i­ties in Falmouth and Birkenhead.


  • 5 Basin looking South. The Submarine Refit Complex (SRC) in the foreground and the larger SSBN dry docks at the top. (Photo: Andy Amor)

  • The size of the 10 Dock (centre) is apparent in this view. Assuming the proposed development proceeds, it will look more like the narrower 9 Dock on the left. HMS Vanguard can just be made out under the scaffolding and covers. (Google, Map data ©2020)

  • The scale of work to rebuild 9 Dock to meet modern nuclear safety standards can be appreciated in this photo from November 2000.

  • 74 docking cradle blocks attach to plinths on the dock floor to support the submarine. The massively strengthened dock walls are clearly visible this view of the work in 9 Dock nearing completion, mid 2001. (Photo: Babcock)

  • 9 Dock with HMS Vanguard in refit (Bottom). 10 dock (centre), 11 and 12 dock (top).  (Photo: Andy Amor, 2019)

  • HMS Albion enters 10 Dock to begin major refit, October 2014.

  • Another era – March 1964. 4 aircraft carriers in Devonport including the mighty HMS Ark Royal (IV) in 10 Dock, plus HMS Eagle, Hermes and Bulwark alongside. RFA Resurgent is in 9 Dock. The minesweepers in the basin at the top of the image are where the Submarine Refit Complex was constructed in the 1970s.

  • The previous HMS Vanguard, The Royal Navy’s last battleship (45,200 tons) in 10 Dock, Devonport. Light cruiser HMS Newfoundland is in the adjacent Number 9 Dock. (Painting by Charles Eddowes Turner, 1947 held by the National Maritime Museum)

Regulations have been con­sid­er­ably tight­ened since 10 Dock was last used for nuclear sub­ma­rine main­te­nance neces­si­tat­ing this major works project which will even­tu­al­ly see Devonport have 4 nuclear-cer­ti­fied dry docks. 9 Dock will be in con­tin­u­al use com­plet­ing the delayed refit and refuel of HMS Vanguard, fol­lowed by Long Overhaul Periods (LOP) for HMS Victorious, Vigilant and Vengeance. Fortunately, it would appear that refu­elling the 3 younger boats can be avoid­ed but each LOP will take around 3 years and it will be the early 2030s before they are com­plet­ed. When the next-gen­er­a­tion SSBN, HMS Dreadnought, arrives in the early 2030s, Number 9 dock will be needed to de-fuel the decom­mis­sioned HMS Vanguard and the other boats as they are replaced. Assuming space can be found, the decom­mis­sioned Vanguards maybe stored afloat for some­time after being de-fuelled but even­tu­al­ly they will need to be dis­man­tled. 9 Dock is the only facil­i­ty large enough and equipped for the work.

With 9 Dock occu­pied by the Vanguard boats well into the future, anoth­er option for main­tain­ing the Dreadnought class will be needed and this is the pri­ma­ry driver behind the project to con­vert 10 Dock, although main­tain­ing the SSNs is also part of the con­sid­er­a­tion. The colos­sal delays to the Astute class con­struc­tion and the delay in start­ing the Dreadnought pro­gramme means that the work on build­ing the Astute replace­ment, known as SSN®, cannot start in Barrow until the late 2030s. It is there­fore likely the first 3 boats HMS Astute, Ambush and Artful may under­go lengthy life exten­sion refits and pos­si­bly refu­elling. This could only be done in 15 Dock at Devonport so anoth­er option for SSN dry-dock­ing will be needed. (Number 14 dock has been des­ig­nat­ed to begin dis­man­tling old SSNs from 2023, a project that could be ongo­ing for up to 40 years.)

Number 10 dock will relieve the pres­sure on the lim­it­ed nuclear sub­ma­rine sup­port facil­i­ties by pro­vid­ing anoth­er site for more rou­tine SSBN and SSN main­te­nance. Although the plans are at an early stage it looks likely they will be approved and work could begin next year. This project fur­ther cements Devonport’s future as a sub­ma­rine refit centre and its cru­cial role in sup­port­ing the nuclear deter­rent.

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