View source for UGM-133 Trident II

{{Short description|US/UK SLBM}}
{{Redirect|Trident II|the French fighter plane|SNCASO Trident}}
{{Use dmy dates|date=April 2017}}
{{Infobox weapon
|is_missile=yes
|name=UGM-133A Trident II
|image =File:Trident II missile image.jpg
|caption = A Trident II launch from a submerged Royal Navy submarine.{{cite needed|date=November 2023}}
|origin= United States
|type=[[Submarine-launched ballistic missile|SLBM]]
|used_by= [[United States Navy]]<br />[[Royal Navy]]
|manufacturer = [[Lockheed Martin Space]]
|unit_cost=$30.9 million (2019)<ref>{{Cite web|url=https://www.navy.mil/Resources/Fact-Files/Display-FactFiles/Article/2169285/trident-ii-d5-missile/|title=The US Navy -- Fact File: Trident II (D5) Missile|website=www.navy.mil|access-date=2022-09-25}}</ref>
|production_date=1983
|service= 1990–present
|engine=Three [[solid-fuel rocket]] motors; first & second stage – [[Thiokol]]/[[Hercules Inc.|Hercules]] solid-fueled rocket; third stage – United Technologies Corp. solid-fueled rocket<ref name="UGM-133">{{cite web |url=http://www.designation-systems.net/dusrm/m-133.html |title=UGM-133 |last=Parsch |first=Andreas |publisher=Directory of U.S. Military Rockets and Missiles |access-date=11 June 2014}}</ref>
|engine_power=
|weight={{convert|130000|lb|abbr=on}}<ref name="Parsch">{{cite encyclopedia |last=Parsch |first=Andreas |title=Trident D-5 |encyclopedia=Encyclopedia Astronautica |url=http://www.astronautix.com/t/tridentd-5.html|archive-url=https://web.archive.org/web/20160804082348/http://www.astronautix.com/t/tridentd-5.html|archive-date=4 August 2016|access-date=11 June 2014}}</ref>
|length={{convert|44|ft|6.6|in|abbr=on}}
|height=
|diameter={{convert|6|ft|11|in|abbr=on}} (1st stage)<ref name="Parsch" />
|wingspan=
|speed=Approximately {{convert|18030|mph|abbr=on}} ({{convert|18030|mph|Mach m/s|abbr=on|disp=output only}})<ref name="Parsch" /> (terminal phase)
|vehicle_range= More than {{convert|12000|km|mi|abbr=on|order=flip}}<ref>{{cite news|url=http://news.bbc.co.uk/2/hi/uk/4438392.stm|title=Fact file: Trident missile|date=23 September 2009|access-date=29 March 2018|via=news.bbc.co.uk}}</ref><ref name="CSIS Missile Threat">{{cite web|url=http://missilethreat.csis.org/missile/trident-d-5/|title=Trident D-5 - Missile Threat|website=csis.org|access-date=29 March 2018}}</ref> (exact is classified)<ref name="DEPARTMENT OF DEFENSE APPROPRIATIONS ACT 1995">{{cite web|title=DEPARTMENT OF DEFENSE APPROPRIATIONS ACT, 1996 (Senate – August 11, 1995)|url=https://fas.org/nuke/guide/usa/slbm/950811-cr.htm|access-date=13 June 2014}}</ref>
|ceiling=
|altitude=
|propellant=[[NEPE-75]]:<ref name="High Energy Rocket Fuels">{{Cite web|title=High Energy Rocket Fuels|url=https://scitoys.com/he_rocket_fuels.html|access-date=2020-12-13}}</ref> [[Nitrate ester]], plasticized [[polyethylene glycol]]-bound [[HMX]], [[Aluminum]], [[ammonium perchlorate]]
|filling=1–12 Mk-5 [[Multiple independently targetable reentry vehicle|RV]]/[[W88]] (475{{nbsp}}kt) or <br /> 1–14 Mk-4 RV/[[W76|W76-0]] (100{{nbsp}}kt) or <br /> 1–14 Mk-4A RV/[[W76|W-76-1]] or(90{{nbsp}}kt) or <br /> unknown Mk-7 RV/[[W93]] (unknown {{nbsp}}kt)<ref name="auto">{{cite journal|title=United States nuclear forces, 2019|journal=Bulletin of the Atomic Scientists|volume=75|issue=3|pages=122–134|last1=Kristensen|first1=Hans M.|last2=Korda|first2=Matt|date=29 April 2019|doi=10.1080/00963402.2019.1606503|bibcode=2019BuAtS..75c.122K|doi-access=free}}</ref> <br /> Single or multiple [[W76|W76-2]] (5–7{{nbsp}}kt)<ref name="W76-2_first_d">{{cite web |url=https://fas.org/blogs/security/2020/01/w76-2deployed/|title=US Deploys New Low-Yield Nuclear Submarine Warhead|publisher=[[Federation of American Scientists|FAS]]|date=29 January 2020|access-date=29 January 2020}}</ref><ref name="W76-2_WP">{{cite news |url=https://www.washingtonpost.com/world/national-security/trump-poised-to-get-new-low-yield-nuclear-weapons/2018/06/13/161b1466-6dac-11e8-9ab5-d31a80fd1a05_story.html|title=Trump poised to get new low-yield nuclear weapons|newspaper=[[Washington Post]]|date=13 June 2018|access-date=29 January 2020}}</ref>
|guidance=MK 6 [[astro-inertial guidance]] which is able to receive [[GPS|Global Positioning System]] updates<ref name="Parsch" /><ref>{{cite web|url=http://www.designation-systems.net/dusrm/m-133.html|title=Lockheed Martin UGM-133 Trident II|website=www.designation-systems.net|access-date=29 March 2018}}</ref>
|steering=[[Thrust vectoring|Single movable nozzle]] actuated by a gas generator
|accuracy=100 m<ref>In Combat, section Smart Weapons, page 13,  Malcolm McCavendish, 1991</ref><ref>[https://i.imgur.com/cx5KJRl.jpg Imgur image]</ref>
|launch_platform=[[Ballistic missile submarine]]
}}

The '''UGM-133A Trident II''', or '''Trident D5''' is a [[submarine-launched ballistic missile]] (SLBM), built by [[Lockheed Martin Space]] in [[Sunnyvale, California]], and deployed with the [[US Navy|United States]] and [[Royal Navy]]. Designed in the 1980s, it was first deployed in March 1990,<ref name="UGM-133" /> and remains in service. The Trident II Strategic Weapons System is an improved SLBM with greater accuracy, payload, and range than the earlier [[UGM-96 Trident I|Trident C-4]]. It is a key element of the U.S. strategic [[nuclear triad]] and strengthens U.S. [[deterrence theory|strategic deterrence]]. The Trident II is considered to be a durable sea-based system capable of engaging many targets. It has payload flexibility that can accommodate various treaty requirements, such as [[New START]]. The Trident II's increased payload allows nuclear deterrence to be accomplished with fewer [[submarine]]s,<ref>{{cite web|title=Trident II (D-5) Sea-Launched Ballistic Missile UGM 133A (Trident II Missile)|url=http://www.dod.mil/pubs/foi/logistics_material_readiness/acq_bud_fin/SARs/2012-sars/13-F-0884_SARs_as_of_Dec_2012/Navy/Trident_II_Missile_December_2012_SAR.pdf|access-date=21 June 2014|archive-url=https://web.archive.org/web/20140112233046/http://www.dod.mil/pubs/foi/logistics_material_readiness/acq_bud_fin/SARs/2012-sars/13-F-0884_SARs_as_of_Dec_2012/Navy/Trident_II_Missile_December_2012_SAR.pdf|archive-date=12 January 2014|df=dmy-all}}</ref> and its high accuracy—approaching that of [[intercontinental ballistic missile|land-based missiles]]—enables it to be used as a [[pre-emptive nuclear strike|first strike]] weapon.<ref>{{cite magazine |title=U.S. Nuclear Primacy and the Future of the Chinese Deterrent |url=https://search.issuelab.org/resource/winter-2007-china-security-journal.html |author1=Lieber, Keir A. |author2=Press, Daryl G. |magazine=China Security |date=Winter 2007 |page=77}}</ref><ref>{{cite book|title=Military persuasion: Deterrence and provocation in crisis and war|author=Cimbala, Stephen J.|year=2010|publisher=Penn State Press|url=https://books.google.com/books?id=rMe9guZoyIUC|access-date=29 January 2016|pages=85–6|quote=By the end of the 1980s, however, the submarine-launched ballistic missile had turned another page. The accuracy of the Trident II (D-5) SLBM, planned as the replacement for the Trident I with Trident II deployments beginning in 1989, was comparable to that of the MX/Peacekeeper ICBM, the most accurate land-based missile in the U.S. strategic arsenal. Owing to its improved accuracy and larger payload compared to its SLBM predecessors, Trident II would be able to attack hardened targets in the Soviet Union that were not previously vulnerable to sea-launched ballistic missiles. Although U.S. planners might assume that these strikes against hardened targets in the Soviet Union would be retaliatory attacks, a Soviet net-assessment of U.S. first-strike capabilities would have to include the improved sea-based missiles.|isbn=978-0271041261}}</ref><ref>{{cite book|title=Tackling Trident|author=Stellan Vinthagen|year=2012|publisher= Irene Publishing|url=https://books.google.com/books?id=hsnJAwAAQBAJ|access-date=29 November 2017|page=41|quote=Although it is accurate enough for a 'first strike' weapon, successive governments have been adamant that the purpose of the current Trident system is as a 'deterrent' against nuclear or similarly cataclysmic attack on Britain. The Trident 'mission' is outlined by the Ministry of Defense: 'In a posture known as Continuous At Sea Defence (CASD), one submarine, armed with up to 16 Trident missiles and up to 48 warheads, is always on deterrent patrol 24 hours a day, 365 days a year' (MoD, 2006).|isbn=9781471751042}}</ref>

Trident II missiles are carried by 14 US {{sclass|Ohio|submarine|5}} and 4 British {{sclass|Vanguard|submarine|0}} submarines, with 24 missiles on each ''Ohio'' class and 16 missiles on each ''Vanguard'' class (the number of missiles on ''Ohio''-class submarines was reduced to 20, by 2017,<ref>{{Cite web|url=https://www.cbo.gov/budget-options/2013/44770|title=Reduce the Number of Ballistic Missile Submarines|website=Congressional Budget Office}}</ref><ref>{{Cite web |title=New Data Shows Detail About Final Phase of US New START Treaty Reductions |url=https://fas.tghp.co.uk/publication/new-start-full-data/ |access-date=2023-12-05 |website=Federation of American Scientists |language=en-US}}</ref> in compliance with the [[New Strategic Arms Reduction Treaty]]). There have been 177 successful test flights of the D5 missile since design completion in 1989,<ref>{{cite web |url=http://www.lockheedmartin.co.uk/us/news/press-releases/2016/september/ssc-space-trdent.html |title=Successful Trident II D5 Missile Flight Test Supports Navy Submarine Certification for Strategic Patrol |publisher=Lockheed Martin |date=13 September 2016 |access-date=26 January 2017 |archive-url=https://web.archive.org/web/20170126023501/http://www.lockheedmartin.co.uk/us/news/press-releases/2016/september/ssc-space-trdent.html |archive-date=26 January 2017 |df=dmy-all }}</ref> the most recent being from {{USS|Maine|SSBN-741}} in February 2020.<ref name="177th_launch">{{Cite web|url=https://www.navy.mil/submit/display.asp?story_id=110802/|title=US Sub Test Fires 2 Ballistic Missiles in Pacific Ocean|access-date=30 May 2022|archive-date=16 July 2020|archive-url=https://web.archive.org/web/20200716221907/https://www.navy.mil/submit/display.asp?story_id=110802%2F}}</ref> There have been fewer than 10 test flights that were failures,<ref>{{cite news |url=https://www.telegraph.co.uk/news/2017/01/23/theresa-may-briefed-trident-missile-test-allegedly-misfired2/ |archive-url=https://ghostarchive.org/archive/20220112/https://www.telegraph.co.uk/news/2017/01/23/theresa-may-briefed-trident-missile-test-allegedly-misfired2/ |archive-date=12 January 2022 |url-access=subscription |url-status=live |title=US Trident failure claims contradict Michael Fallon |first1=Kate |last1=McCann |first2=Peter |last2=Dominiczak |first3=Steven |last3=Swinford |newspaper=The Daily Telegraph |date=23 January 2017 |access-date=26 January 2017}}{{cbignore}}</ref> the most recent being from {{HMS|Vanguard|S28|6}} off the coast of Florida in January 2024.<ref name="UKDJ2024">{{cite web|title=British Trident missile test launch fails for second time|url=https://ukdefencejournal.org.uk/british-trident-missile-test-launch-fails-for-second-time/|publisher=UK Defence Journal|access-date=21 February 2024|date=21 February 2024}}</ref> The D5 is the sixth in a series of missile generations deployed since the sea-based deterrent program began 60 years ago. The [[Trident (missile)#D5LE (D5 Life Extension Program)|Trident D5LE (life-extension)]] version will remain in service until 2042.<ref>{{cite web|url=https://www.armscontrol.org/factsheets/USNuclearModernization |title=U.S. Nuclear Modernization Programs  |publisher=Arms Control Association|date=August 2016|access-date=6 September 2016}}</ref>

==History==
[[File:151107-N-ZZ999-001 - SLBM being launched from USS Kentucky.jpg|thumb|left|[[USS Kentucky (SSBN-737)|USS ''Kentucky'']] firing a Trident II SLBM in 2015 as part of the [[Demonstration and Shakedown Operation (DASO)|DASO 26]] test launch]]

The Trident II was designed with greater range and payload capacity than its predecessor ([[UGM-96 Trident I|Trident C-4]]). In 1972, the US Navy projected an [[initial operating capability]] (IOC) date of 1984. The US Navy shifted the IOC date to 1982. On 18 October 1973, a Trident program review was administered. On 14 March 1974, the US Deputy Secretary of Defense disseminated two requirements for the Trident program. The first was an accuracy improvement for the Trident C-4. The second requirement asked for an alternative to the C-4, or a new Trident II missile with a larger first-stage motor than the C-4.

The U.S. Navy conducted studies to determine whether the more expensive Trident II could be constructed similarly to the US Air Force's [[LGM-118A Peacekeeper|MX ICBM]], primarily to decrease budget costs. It was established that the Trident II would be {{convert|83|in|cm}} in diameter and {{convert|44|ft|m}} in length in order to match the performance of the existing [[LGM-118A Peacekeeper|MX ICBM]]. Modifications to the guidance system, electronics hardening, and external protective coatings were incorporated into the design. While this satisfied the Navy's study requirements, it did not accommodate the US Air Force payload requirements.

Propulsion stages were proposed to be used between the first stage and second stage motors, effectively making the Trident II a longer three-stage missile than the C-4. Studies were delayed in 1978 when Congress only approved $5&nbsp;million of the suggested $15&nbsp;million for the Navy and Air Force program studies. By December 1978, the Navy's and the Air Force's own studies agreed with each other that a similar missile structure would not achieve desired savings. It was determined that the Navy and Air Force would maintain and be responsible for their own unique weapon systems. The US Navy continued with its own design of the Trident II.

In March 1980, [[United States Secretary of Defense|US Secretary of Defense]] [[Harold Brown (Secretary of Defense)|Harold Brown]] proposed an increased level of funding for the submarine-launched ballistic missile modernization, emphasizing increased accuracy. The [[United States House Committee on Armed Services|House Armed Services Committee]] (HASC) recommended no funding, while the [[United States Senate Committee on Armed Services|Senate Armed Services Committee]] (SASC) recommended full funding of $97&nbsp;million. The SASC asked for a plan incorporating "the fullest possible competition . . . [and] should consider competing among contractors for each major component, including the integrated missile." $65&nbsp;million was awarded for the submarine-launched ballistic missile modernization.

On 2 October 1981, President Reagan called for the modernization of the strategic forces.<ref name="Remarks and a Question-and-Answer Session With Reporters on the Announcement of the United States Strategic Weapons Program">{{cite web |url=http://www.reagan.utexas.edu/archives/speeches/1981/100281c.htm |title=Remarks and a Question-and-Answer Session With Reporters on the Announcement of the United States Strategic Weapons Program |publisher=National Archives and Records Administration |access-date=24 December 2014 |archive-date=24 September 2015 |archive-url=https://web.archive.org/web/20150924085223/http://www.reagan.utexas.edu/archives/speeches/1981/100281c.htm }}</ref> The Defense Department directed the Navy to fund all development of the Trident II D5 missile with a December 1989 IOC. All research and development efforts would be directed toward "a new development, advanced technology, high accuracy Trident II D5 system." In December 1982, [[United States Deputy Secretary of Defense|Deputy SECDEF]] [[Frank Carlucci]] advised the Secretary of Defense [[Caspar Weinberger]] to include funding for a new reentry vehicle–warhead combination for Trident II. The reentry vehicle was to be designated as the [[Multiple independently targetable reentry vehicle|Mk 5]], which was to have a greater yield than the Mk 4. The development contract for Trident II was issued in October 1983. On 28 December 1983, the deputy SECDEF authorized the Navy to proceed with full-scale engineering development of the Trident II D5.

An initial series of 19 land-based Trident II launches took place from [[Cape Canaveral Space Launch Complex 46|Cape Canaveral Launch Complex 46]] from 15 January 1987 to 27 January 1989.<ref>{{cite web|url=http://www.astronautix.com/t/tridentd-5.html|archive-url=https://web.archive.org/web/20160804082348/http://www.astronautix.com/t/tridentd-5.html|archive-date=4 August 2016|title=Trident D-5|website=www.astronautix.com|access-date=29 March 2018}}</ref> The first submarine launch was attempted by {{USS|Tennessee|SSBN-734|6}},<ref name="Parsch" /> the first D-5 ship of the ''Ohio'' class, on 21 March 1989 off the coast of [[Cape Canaveral]], Florida. The launch attempt failed four seconds into the flight because the plume of water following the missile rose to a greater height than expected, and water was in the nozzle when the motor ignited. Once the problem was understood, relatively simple changes were quickly made, but the problem delayed the initial operating capability of Trident II until March 1990.<ref name="UGM-133" /><ref>{{Cite journal |last=Pope |first=Brian |jstor=23623966 |title=Trident II Missile Fails First Trial at Sea |date=April 1989 |journal=Arms Control Today |publisher=Arms Control Association |volume=19 |issue=3 |page=27 }}</ref> IOC for Strategic Weapons Facility Pacific (SWFPAC) was completed on schedule in 2001, allowing Trident II SSBN to be deployed in the Pacific theater.

In 1980, the United Kingdom adopted the [[UGM-96 Trident I|Trident I C-4]] missile as part of its [[Trident nuclear programme|Trident nuclear program]].<ref>{{cite web|title=THE UNITED KINGDOM TRIDENT PROGRAMME|date=2 April 2013 |url=https://www.dartmouth.edu/~dpress/docs/Press_US_Nuclear_Primacy_CS.pdf|access-date=12 December 2017|quote=On 15 July 1980 my predecessor announced the Government's choice of the Trident submarine-launched ballistic missile system to replace the United Kingdom's current Polaris-equipped strategic deterrent force.}}</ref>

==Design==
The Trident II is a [[multistage rocket|three-stage rocket]], each stage containing a [[solid-fuel rocket]] motor. The first motor is made by [[Northrop Grumman]]. This first stage incorporates a solid propellant motor, parts to ensure first-stage ignition, and a [[Thrust vectoring|thrust vector control]] (TVC) system. The first-stage section, compared to the [[Trident C-4]], is slightly larger, allowing increased range and a larger payload. In addition to a larger motor, the D-5 uses an advanced and lighter fuel binder ([[polyethylene glycol]]) than the C-4.<ref name="Trident I C-4 FBM / SLBM">{{cite web|title=Trident I C-4 FBM / SLBM|url=https://fas.org/nuke/guide/usa/slbm/c-4.htm|access-date=13 June 2014}}</ref> This fuel is more commonly known as [[Solid-fuel rocket#Composite modified double base propellants|NEPE-75]]. (NEPE stands for ''nitrate ester plasticized polyether'', the 75 represents that the fuel contains 75% solids.)<ref name="fas.org">{{cite web|title=Trident II D-5 Fleet Ballistic Missile|url=https://fas.org/nuke/guide/usa/slbm/d-5.htm|access-date=13 June 2014}}</ref><ref>{{Patent|US|8778103|Energetic compositions including nitrate esters, methods of forming such energetic compositions, and articles including such energetic compositions.}}</ref><ref name="High Energy Rocket Fuels"/> The solid components bound by fuel binder are [[HMX]], [[aluminum]], and [[ammonium perchlorate]].<ref name="High Energy Rocket Fuels"/>

Both the first- and second-stage motors are connected by an interstage casing, which contains electronic equipment and ordnance for separation during flight. The second stage also contains a motor made by Thiokol and Hercules Inc., parts to ensure the second-stage ignition, and a TVC system. The first and second stages are both important to the structural integrity of the missile. To ensure that the stages maintain a maximal strength-to-weight ratio, both stages are reinforced by a [[carbon-fiber-reinforced polymer]] hull.<ref name="fas.org"/>

The second and third-stage sections are connected by an integrated equipment/adapter section (ES). The equipment/adapter section is modified to be shorter and more compact than the C-4's adapter section.<ref name="Trident I C-4 FBM / SLBM"/> The D-5's equipment section contains critical guidance and flight control avionics, such as the Mk 6 navigation system. The equipment section also contains the third-stage TVC system, ordnance for ejecting from the second-stage motor, and the MIRV platform. The nose fairing shields the payload and third-stage motor. Mounted within the nose cap (above the nose fairing) is an extendable [[drag-reducing aerospike|aerospike]].<ref>{{cite web|title=TRIDENT II (D5) DIMENSIONS AND JOINTS|url=https://fas.org/nuke/guide/usa/slbm/d5_04.gif|access-date=13 June 2014}}</ref> This aerospike effectively decreases drag by 50%. The third-stage hull is also reinforced by [[carbon-fiber-reinforced polymer|carbon fiber]] and [[kevlar]].<ref name="fas.org"/>

The Trident II is the first missile of the [[United States Navy|US Navy's]] Fleet Ballistic Missile program to incorporate a [[3D printing|3D printed]] component.<ref name="3d print">{{cite web|title=Big Time Savings on Small Part: First 3-D-printed Component Flies on U.S. Navy's Trident II D5 Missile|url=https://www.lockheedmartin.com/us/news/press-releases/2016/march/ssc-space-trident.html|access-date=1 January 2018}}</ref>

While Lockheed Martin is the prime contractor, a variety of corporations work on the Trident II. For example, in October 2020, Boeing was contracted for maintenance, rebuilding and technical services for the Trident II navigation subsystem,<ref name="auto1">{{Cite web|title=Contracts for October 1, 2020|url=https://www.defense.gov/Newsroom/Contracts/Contract/Article/2369073//|access-date=2021-01-19|website=U.S. DEPARTMENT OF DEFENSE|language=en-US}}</ref> and Northrop Grumman was contracted for engineering support and integration for the Trident II and relevant submarines at sites and shipyards from Sunnyvale, California, and Bangor, Washington, to Kings Bay, Georgia, and Cape Canaveral, Florida, among other locales.<ref name="auto1"/> Peraton was contracted for program support services on the Trident II reentry subsystem,<ref>{{Cite web|title=Contracts for October 2, 2020|url=https://www.defense.gov/Newsroom/Contracts/Contract/Article/2370617//|access-date=2021-01-19|website=U.S. DEPARTMENT OF DEFENSE|language=en-US}}</ref> and Systems Planning & Analysis Inc. was contracted for Trident II technical services, program support, assessments, special studies, and systems engineering.<ref name="auto1"/>

===Sequence of operation===
[[File:DASO 25 Video (Cleared for Release) VP8 001 Trident II UGM 133A Test Launch 02 June 2014.webm|thumb|thumbtime=1:46|right|US Navy test-firing two Trident II D-5 UGM-133A missiles in the Atlantic Missile Range, June 2014 (DASO 25 SSBN 736) during a [[Demonstration and Shakedown Operation (DASO)|Demonstration and Shakedown Operation]].]]
Before the launch sequence is initiated, the on-board MARK 6 navigation system is activated. The specified mission trajectory is loaded onto the flight computer.<ref name="Mark 6">{{cite web|last=Jackson|first=Todd|title=Modifying the MARK 6 Guidance System Part 1|url=https://www.evaluationengineering.com/modifying-the-mark-6-guidance-system-part-1|access-date=12 December 2017}}</ref>

Once the launch command is given, a steam generator system is activated, igniting a gas generator<ref name="FBM Elements">{{cite web|title=FBM Functional Elements|url=http://www.ssp.navy.mil/fb101/functionalelements.html#IV|access-date=12 December 2017}}</ref> whose exhaust is fed into cooling water, causing expanding gas within the launch tube to force the missile upward, and out of the [[Ballistic missile submarine|submarine]].<ref name="FBM Elements" /> Within seconds, the missile breaches the surface of the water and the first-stage [[Thrust vectoring|Thrust Vectoring Control]] (TVC) subsystem ignites. This enables hydraulic actuators attached to the first-stage nozzle. Soon after, the first-stage motor ignites and burns for approximately 65 seconds until the fuel is expended; in addition, an [[drag-reducing aerospike|aerospike]] atop the missile deploys shortly after first-stage ignition to shape airflow.  When the first-stage motor ceases operation, the second-stage TVC subsystem ignites. The first-stage motor is then ejected by ordnance within the interstage casing.<ref name="Santa Cruz Facility Brochure">{{cite web|title=Santa Cruz Facility Brochure|url=http://www.lockheedmartin.com/content/dam/lockheed/data/space/documents/tridentdiid5/SantaCruzFacility%20Brochure.pdf|access-date=23 June 2014}}</ref><ref>{{cite web|title=Trident II D-5 Fleet Ballistic Missile|url=http://www.globalsecurity.org/wmd/systems/d-5-specs.htm|access-date=23 June 2014}}</ref>

Once the first stage is cleared, the second-stage motor ignites and burns for approximately 65 seconds. The [[Payload fairing|nose fairing]] is then jettisoned, separating from the missile. When the nose fairing is clear of the missile, the third-stage TVC subsystem ignites, and ordnance separates the second-stage motor. The third-stage motor then ignites, pushing the equipment section the remaining distance (approx. 40 seconds) of the flight. When the third-stage motor reaches the targeted area, the Post Boost Control System (PBCS) ignites, and the third-stage motor is ejected.

The [[astro-inertial guidance]] uses [[star positioning]] to fine-tune the accuracy of the [[inertial guidance]] system after launch. As the accuracy of a missile is dependent upon the guidance system knowing the exact position of the missile at any given moment during its flight, the fact that stars are a fixed reference point from which to calculate that position makes this a potentially very effective means of improving accuracy. In the Trident system, this was achieved by a single camera that was designed to spot just one star in its expected position. If it was not quite aligned to where it should be, it would indicate that the inertial system was not precisely on target and a correction would be made.<ref>{{cite web|title=Trident II D-5 Fleet Ballistic Missile|url=http://www.globalsecurity.org/wmd/systems/d-5-features.htm|access-date=23 June 2014}}</ref>

The equipment section, with the [[Multiple independently targetable reentry vehicle|MIRV]], then aims the reentry vehicles (RV) towards the earth. The payload is then released from the MIRV platform. To prevent the PBCS correctional thrust from interfering with the RV when released, the equipment section initiates the Plume Avoidance Maneuver (PAM). If the RV will be disrupted by the PBCS nozzle's thrust, the nearest nozzle will shut off until the RV is away from the MIRV. The PAM is used only when a nozzle's plume will disrupt the area near an RV. The PAM is a specialized design feature added to the Trident II to increase accuracy.<ref name="Santa Cruz Facility Brochure"/>

===Warheads===
In US service Trident II can be loaded with up to eight Mk-5 [[Multiple independently targetable reentry vehicle|RV]]s with 475-kt [[W88]] warheads, up to fourteen Mk-4A RVs with 90-kt [[W76|W76-1]] warheads, and up to fourteen Mk-4A RVs with 5–7-kt [[W76|W76-2]] warheads. In practice, each missile on average carries four warheads due to the warhead limitations placed by the [[New START]] treaty.<ref>US State Department, New START Dis-aggregate data for 2020.  https://www.state.gov/wp-content/uploads/2020/07/06-25-2020-FACTSHEET-Public-Release-of-Dis-aggregate-Data.pdf. There are 927 warheads deployed on 210 Trident II D5 missiles, or an average of 4.4 warheads per missile.  Some missiles are "de-MIRVed" and equipped with a single W76-2 warhead, which depresses the overall average.</ref>

The system previously carried the Mk-4 RV with a 100{{nbsp}}kt W76-0 warhead, but beginning in September 2008 W76-0s were converted to W76-1s. This process was completed by December 2018.<ref>[https://www.defensenews.com/space/2019/01/23/work-completed-on-navys-upgraded-nuclear-warhead/ Work completed on Navy's upgraded nuclear warhead]. ''Defense News''. 24 January 2019.</ref> Conversion from the W76-0 to W76-1 involved fitting the warheads with a new RV (the Mk-4A), replacing age limited components and fitting the warhead with a new MC4700 arming, fusing and firing (AF&F) system. The MC4700 AF&F system (dubbed the "super fuze") significantly improves warhead kill probabilities against hardened targets such as silos or bunkers. The W76-2 is also fitted with the Mk-4A RV and MC4700 fuze.<ref name = "designation-systems.net">{{cite web | url = http://www.designation-systems.net/dusrm/m-133.html | title = Lockheed Martin UGM-133 Trident II | access-date = 12 December 2013 }}</ref><ref name="auto"/><ref>{{cite web|url=https://fas.org/nuke/guide/usa/Brief2016_ACA.pdf|title=Nuclear Modernization, Enhanced Military Capabilities, and Strategic Stability|website=[[Federation of American Scientists]]|last1=Kristensen|first1=Hans M.|last2=McKinzie|first2=Matthew|last3=Postol|first3=Theodore|date=6 June 2016|access-date=18 November 2019}}</ref>

In the [[National Nuclear Security Administration]]'s 2021 budget request, the agency requested US$53m to begin development of a new [[W93]] warhead for use on Trident II and US$32 million to begin development of a new Mk-7 RV. If approved, the W93 will be the first new nuclear weapon system to receive a type designation since the end of the Cold War. It is unclear if the W93 will replace the W76-1, the W88 or both warheads.<ref>{{cite web | url =https://www.defensenews.com/smr/nuclear-arsenal/2020/02/24/inside-americas-newly-revealed-nuclear-ballistic-missile-warhead-of-the-future/| title =Inside America's newly revealed nuclear ballistic missile warhead of the future| date = 24 February 2020| access-date = 9 March 2020}}</ref>

In UK usage Trident II missiles are equipped with a warhead called Holbrook<ref name=BritCom/> and have a maximum yield of 100{{nbsp}}kt.<ref>{{cite web |url=https://nuclearweaponarchive.org/Uk/UKArsenalRecent.html|title=Britain's Nuclear Weapons; The Current British Arsenal|date=30 April 2001|website=The Nuclear Weapon Archive|publisher=Carey Sublette|access-date=2020-03-08|quote=The Trident warheads also offer multiple yields - probably 0.3 kt, 5-10 kt and 100 kt - by choosing to fire the unboosted primary, the boosted primary or the entire "physics package".}}</ref> The UK government insists the warhead is a British design, but analysts believe that it is largely based on the US W76 design.<ref name=BritCom/><ref>{{cite web|title=Britain's Next Nuclear era|url=https://fas.org/blogs/security/2006/12/britains_next_nuclear_era/|publisher=Federation of American Scientists|access-date=8 March 2020|date=7 December 2006}}</ref> In 2011 it was reported that British warheads would receive the new Mk 4A reentry vehicles and some or all of the other upgrades that US W76 warheads were receiving in their W76-1 Life Extension Program.<ref>Kristensen, Hans. [https://fas.org/blog/ssp/2011/04/britishw76-1.php "British Submarines to Receive Upgraded US Nuclear Warhead."] {{Webarchive|url=https://web.archive.org/web/20110406231928/http://www.fas.org/blog/ssp/2011/04/britishw76-1.php |date=6 April 2011 }} ''FAS'', 1 April 2011.</ref> Some reports suggested that British warheads would receive the same arming, fusing and firing system (AF&F) as the US W76-1.<ref>{{cite web |title=Trident more effective with US arming device, tests suggest|website=[[TheGuardian.com]] |date=6 April 2011 |url=https://www.theguardian.com/uk/2011/apr/06/trident-us-arming-system-test |access-date=8 March 2020}}</ref> Under a 1958 agreement, the US supplies the UK with blueprints of its own warhead designs but the design, manufacture and maintenance of UK warheads are purely a UK responsibility. AWE is currently developing a new warhead to replace the existing Holbrook warhead with deployment expected in the 2030s.<ref name = "BritCom">{{cite web | url =https://www.defensenews.com/global/europe/2020/02/25/britain-confirms-new-nuclear-warhead-project-after-us-officials-spill-the-beans/| title =Britain confirms new nuclear warhead project after US officials spill the beans| date =25 February 2020 | access-date = 8 March 2020}}</ref>

==Additional specifications==
* Range (exact is classified): <br />Full load: ~{{convert|7600|km}}<ref name="Range dependency"/> <br />Reduced load: ~{{convert|12000|km}}<ref name="Range dependency"/>
* Guidance system: The MK 6 [[Astro-inertial guidance]] navigation system. Inertial guidance is most favored for the initial guidance and reentry vehicles of [[Intercontinental ballistic missile|strategic missiles]], because it has no external signal and cannot be [[countermeasure|jammed]].<ref>Siouris, George. ''Missile Guidance and Control Systems.'' 2004</ref>
* [[Circular error probable|CEP]]: Requirement: <{{convert|90|m}}.<ref>{{cite thesis |degree=Master's |last1=Chinworth|first1=William C.|date=15 March 2006|title=The Future of the Ohio Class Submarine |publisher=U.S. Army War College |url=https://apps.dtic.mil/dtic/tr/fulltext/u2/a449427.pdf |archive-url=https://web.archive.org/web/20200927074547/https://apps.dtic.mil/dtic/tr/fulltext/u2/a449427.pdf |url-status=live |archive-date=27 September 2020 |via=Defence Technical Information Center}}</ref>  (Information from flight tests is classified.)

{| class="wikitable mw-collapsible"
|+ class="nowrap" | Mk-5 RV (175&nbsp;kg each) offloading effects{{clarify|date=June 2021}} on D-5 range<ref name="Range dependency">{{cite journal|last1=Harvey|first1=John R.|last2=Michalowski|first2=Stefan|date=21 December 2007|title=Nuclear weapons safety: The case of trident|url=http://scienceandglobalsecurity.org/archive/sgs04harvey.pdf|journal=Science & Global Security|volume=4|issue=1|pages=303|doi=10.1080/08929889408426405}}</ref>
|-
! Mk-5 RVs
! Throw-weight (kg)
! D-5 range (km)
! Increase in range (%)
|-
! 8
| 2,700<ref>[[Payload fairing|Nose fairing]] and end cap weights (180 kg) are subtracted.</ref> || 7,593 || nominal
|-
! 7
| 2,525 || 8,278 || 9
|-
! 6
| 2,350 || 9,111 || 20
|-
! 5
| 2,175 || 10,148 || 34
|-
! 4
| 2,000 || 11,519 || 52
|-
! 3
| 1,825 || 13,482 || 78
|}

==Operators==
[[File:UGM-133 operators.png|thumb|400px|Map with UGM-133 operators in blue]]
{{multiple image
 | align = right
 | total_width = 420
 | image1 = USS Kentucky (SSBN-737).jpg
 | width1 = 597| height1 = 444
 | alt1 = USS ''Kentucky''
 | caption1 = {{USS|Kentucky|SSBN-737|6}}, an ''Ohio''-class submarine of the US Navy

 | image2 = HMS Vigilant MOD 45157568.jpg
 | width2 = 3000 | height2 = 2250
 | alt2 = HMS ''Vigilant''
 | caption2 = {{HMS|Vigilant|S30|6}}, a ''Vanguard''-class submarine of the Royal Navy

 | footer = 
}}
{{multiple image
 | align = right
 | total_width = 420
 | image1 = Artist rendering of a Columbia-class ballistic missile submarine, 2019 (190306-N-N0101-125).jpg
 | width1 = 800| height1 = 578
 | alt1 = ''Columbia''-class
 | caption1 =

 | image2 = Successor-class submarine program.jpg
 | width2 = 800 | height2 = 548
 | alt2 = ''Dreadnought''-class
 | caption2 =

 | footer = Artists' impressions of ''Columbia''-class (left) and ''Dreadnought''-class (right)
}}

The [[Royal Navy]] operates its missiles from a shared pool, together with the Atlantic squadron of the [[U.S. Navy]] ''Ohio''-class SSBNs at [[Naval Submarine Base Kings Bay|King's Bay, Georgia]]. The pool is co-mingled and missiles are selected at random for loading on to either nation's submarines.<ref>{{cite web|url=https://ukdjcdn-b4d.kxcdn.com/uploads/2014/07/UK-Nuclear-Deterrent-FOI-Response.pdf|title=Freedom of information request about the UK nuclear deterrent|date=19 July 2005|access-date=25 January 2017|publisher=Ministry of Defence|archive-url=https://web.archive.org/web/20161030002309/https://ukdjcdn-b4d.kxcdn.com/uploads/2014/07/UK-Nuclear-Deterrent-FOI-Response.pdf|archive-date=30 October 2016|df=dmy-all}}</ref><ref name="UKDJ2017">{{cite web|title=How serious was the Trident missile test failure?|url=https://ukdefencejournal.org.uk/serious-trident-missile-test-failure/|publisher=UK Defence Journal|access-date=24 January 2017|date=22 January 2017}}</ref>

===Trident II missile submarines===
{|
|-
| style="vertical-align:top; width:3%;"|
{{navy|USA}}
*[[Ohio-class submarine|''Ohio''-class submarine]]
**{{USS|Henry M. Jackson|SSBN-730|2}}
**{{USS|Alabama|SSBN-731|2}}
**{{USS|Alaska|SSBN-732|2}}
**{{USS|Nevada|SSBN-733|2}}
**{{USS|Tennessee|SSBN-734|2}}
**{{USS|Pennsylvania|SSBN-735|2}}
**{{USS|West Virginia|SSBN-736|2}}
**{{USS|Kentucky|SSBN-737|2}}
**{{USS|Maryland|SSBN-738|2}}
**{{USS|Nebraska|SSBN-739|2}}
**{{USS|Rhode Island|SSBN-740|2}}
**{{USS|Maine|SSBN-741|2}}
**{{USS|Wyoming|SSBN-742|2}}
**{{USS|Louisiana|SSBN-743|2}}
*[[Columbia-class submarine|''Columbia''-class submarine]] (planned)
**{{USS|District of Columbia|SSBN-826|2}}
**{{USS|Wisconsin|SSBN-827|2}}
| style="vertical-align:top; width:5%;"|
{{navy|UK}} 
*[[Vanguard-class submarine|''Vanguard''-class submarine]]
**{{HMS|Vanguard|S28|2}}
**{{HMS|Victorious|S29|2}}
**{{HMS|Vigilant|S30|2}}
**{{HMS|Vengeance|S31|2}}
*[[Dreadnought-class submarine|''Dreadnought''-class submarine]] (planned)
**[[HMS Dreadnought (Dreadnought-class submarine)|''Dreadnought'']]
**''Valiant''
**''Warspite''
**''King George VI''
|}

==See also==
* [[JL-2]]
* [[KN-11|Pukkuksong-1]]
* [[M45 (missile)]]
* [[M51 (missile)]]
* [[R-29RMU Sineva]]
* [[R-29RMU2 Layner]]
* [[R-39 Rif]]
* [[RSM-56 Bulava]]
* [[K Missile family]]

==References==
{{Reflist|30em}}

== External links ==
* {{Commons category-inline|UGM-133A Trident II D-5}}

{{US missiles}}

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