Defence research Version 1.0 · Last updated 17 April 2026

The Defence Nuclear Enterprise Dependency Atlas

A comprehensive catalogue, network model and severance simulator for the United Kingdom's operational, technical, material, scientific, legal and human dependencies on the United States across the nuclear deterrent chain — from treaty scaffolding to tritium gas transfer systems.
Compiled from open sources — MDA Command Papers · MOD DNE Command Paper (2024) · NAO Dreadnought reports · Nuclear Information Service briefings · RUSI · BASIC · FAS · CRS · Arms Control Today · NNSA fact sheets

Strategic Overview

Summary · Heatmap · Methodology

Dependencies by domain 16 Domains · Dependencies

Critical (4) High (3) Moderate (2) Cost-saving (1)

The architecture in one paragraph Editorial

The United Kingdom operates the Western world's most deeply integrated nuclear weapons programme with another state. The 1958 Mutual Defence Agreement — made indefinite on 14 November 2024 — is its constitutional backbone. The 1963 Polaris Sales Agreement governs the delivery system. Through these, Britain leases its Trident D5 missiles from a common pool in Georgia, imports Mk4A reentry bodies whose design heritage is American, buys Mk7 aeroshells for its next warhead from the US, co-designs the missile compartment for its next-generation SSBN with the US Navy, sources tritium from the Savannah River Site, participates in US sub-critical experiments at Nevada, and sustains a network of Joint Working Groups (48 of which have existed since 1959, with a substantial subset active and several still classified) that cover everything from warhead electrical systems to transport safety. The ability to operate, certify and renew the deterrent rests on a scaffold of roughly — distinct US dependencies.

Analytically, this tool distinguishes operational from programmatic from scientific from material dependencies, and scores each along four axes: criticality, severability, time-to-impact, and whether the UK has a domestic fallback.

Severability vs. criticality Scatter

↑ more critical → easier for UK to replace

Top exposure — highest stakes, least substitutable Ranked

The dependencies in the top-left quadrant of the scatter — most critical, hardest to replace. Ranked by composite exposure score. Click for detail.

Modernisation is deepening dependency, not diluting it Analytical

Astraea (A21/Mk7)
Parallel with W93; Mk7 aeroshell from US; certified without live tests using US archival data.
The replacement warhead is more US-entangled by design than Holbrook was — reciprocal design convergence is a deliberate programme aim.
Dreadnought SSBN
Jointly designed missile compartment, jointly sustained fire control, jointly managed missile pool.
CMC is a co-production with a US-directed design authority. Production-line integration with Columbia is a scheduling link, not just a technical one.
PWR3 & AUKUS
Reciprocal naval propulsion exchange (2024 MDA amendment); SSN-AUKUS binds three industrial bases.
The 2024 MDA reciprocity on reactor cooperation, and the 2025 AUKUS NNPA, extend propulsion entanglement into the next century.
Stewardship without testing
Orpheus at NNSS, ASC codes, NIF access, archival test data — all US-hosted or US-owned.
No-test certification of Astraea is only achievable because of US infrastructure. A UK-alone equivalent is not on the horizon.

Each leg of the current modernisation cycle — warhead, platform, reactor, stewardship — increases the depth, specificity and near-term irreversibility of UK dependency on the United States, compared with the systems being replaced. That is the opposite of how 'sovereignty' is sometimes presented in political rhetoric; it is the quiet logic of the MDA becoming indefinite in November 2024.

Selected structural findings Analytical

    Method note. The catalogue draws exclusively on open sources: the 2024 MDA Command Paper (Cm 1135), the March 2024 MOD Delivering the UK's nuclear deterrent as a national endeavour Command Paper, NAO reports on the Dreadnought and AWE programmes, Hansard, Pentagon contract announcements, NNSA fact sheets, and the scholarly literature. Where there are two or more sources for a claim, the stronger/more recent is used. Classification is by the compiler; scoring is inherently judgemental. This is not a substitute for an internal DNO dependency register; it is a structured open-source approximation for analytical and journalistic use.

    Dependency Catalogue

    Click any row for full dossier
    ID ▾ Dependency ▾ Domain ▾ Criticality ▾ Severability ▾ Time-to-impact ▾

    Dependency Network

    Force-directed · Drag nodes · Click to inspect

    Filters

    How to read this graph

    Nodes are individual dependencies, colour-coded by criticality. Larger nodes have more downstream effects if severed. Lines represent direct dependencies — a link from Mk4A aeroshell to warhead certification means the former is required for the latter. Clusters reveal the natural sub-systems of the enterprise: the warhead stack, the delivery system, the reactor lineage, the scientific substrate.

    Critical · cannot operate without High · major degradation Moderate · significant cost/effort Cost-saving
    Hover a node for detail

    Leverage Map

    Which US entities hold the most concentrated leverage over the UK deterrent
    Reading this view. Each row is a US entity. The aggregate leverage score combines the number of dependencies the entity holds, their criticality, and their severability (lower severability = higher leverage). The larger the score, the greater the entity's unilateral ability to degrade UK deterrent operations by constraining cooperation. Click a row to see the specific dependencies.
    Rank US entity Dependencies held Avg. criticality Avg. severability Leverage score
    Note. "Entity" here is a working approximation. Some dependencies implicate multiple entities (e.g. Sandia + LANL on an AF&F item); the primary responsible entity is used. Historical dependencies (e.g. 1960–79 HEU transfers) are included where they continue to shape present capability. A high leverage score does not mean such leverage would be exercised — it quantifies what an entity could, in principle, constrain.

    Historical Timeline

    1958 → 2026 · Agreements, platforms, materials, warheads
    Agreement Platform Warhead Material / Facility Structural event

    Severance Model

    Interactive · What breaks if cooperation narrows or ends
    Click individual dependencies to sever them, or pick a scenario. The model recalculates residual UK deterrent capability by domain, with first- and second-order impacts and rough time-to-degradation.

    Residual UK Deterrent Capability Score Model

    100
    Full US cooperation — baseline

    Cascade: projected impacts over time

    Preset scenarios

    Toggle individual dependencies

    Sources & Method

    Bibliography · Open-source only

    Methodology

    This atlas was built by triangulating official UK and US documents with specialist analytic literature. The foundational texts are the 2024 MDA Command Paper and explanatory memorandum (Cm 9906 / Cm 1135), the MOD's March 2024 Delivering the UK's nuclear deterrent as a national endeavour command paper (the first full DNE statement to Parliament), NAO reports on Dreadnought acquisition and the AWE infrastructure programme, and Pentagon contract announcements identifying specific US–UK deliverables. These are supplemented by FAS Nuclear Notebook entries (Kristensen, Korda, Johns), RUSI Whitehall papers, BASIC commentary, Arms Control Today, CRS reports for Congress (including IF11999 on AUKUS cooperation), Nuclear Information Service briefings including on JOWOGs and MDA material transfers, and the standard scholarly literature (Mackby & Cornish; Baylis; Stoddart).

    Criticality scoring (1–4) reflects: (4) dependencies without which continuous at-sea deterrence could not be maintained on any realistic timescale; (3) dependencies whose loss would force rapid, costly, degraded substitution and likely multi-year gaps; (2) dependencies that would impose significant cost or technical compromise; (1) dependencies that primarily save money or effort. Severability (1–5) reflects how plausible an independent UK substitute is within a decade on the resources available. Time-to-impact reflects how quickly severance would produce an operational effect on deterrent availability or certification.

    Primary sources & key analytic works