Background
Naval nuclear propulsion combines two technologies: pressurized water reactor (PWR) nuclear plants providing heat, and conventional steam turbine plants converting that heat to mechanical (or electrical) propulsion power. From a marine engineering standpoint, every nuclear-powered warship is mechanically a steam turbine ship — the nuclear reactor simply replaces the conventional boiler.
Six nations operate nuclear naval vessels, each with distinctive fleet structures, reactor designs, and strategic priorities. Plus Russia operates the world’s only civilian nuclear fleet through Atomflot’s icebreaker operations.
This article surveys the global naval nuclear fleet as of 2025-2026, reactor designers, and the propulsion architectures.
United States Navy (2025)
The largest naval nuclear fleet:
Submarines (~70 active)
- SSNs (~50 attack submarines):
- Los Angeles-class: 23 active boats (declining as Virginia replacements deliver)
- Seawolf-class: 3 boats (Seawolf, Connecticut, Jimmy Carter)
- Virginia-class: 23 active as of July 2025 (Block I-V; Block VI in procurement)
- SSBNs: 14 Ohio-class ballistic missile submarines (some converting to Columbia replacements)
- SSGNs: 4 Ohio-class converted to Tomahawk-armed cruise missile boats
Aircraft carriers (CVNs)
- Nimitz-class: 10 carriers (USS Nimitz through USS George H.W. Bush)
- Gerald R. Ford-class: USS Gerald R. Ford (commissioned 2017); follow-on units in build/procurement
In procurement
- Multi-year buy of 10 Block VI Virginia-class
- 5 Columbia-class SSBN replacements for Ohio
Reactor designers
US Naval Reactors program designs and certifies reactors via Westinghouse Electric and BWX Technologies (BWXT) as principal contractors:
- A1B: Ford-class CVN
- A4W: Nimitz-class CVN
- S6G/S9G: Los Angeles / Virginia SSNs
- S8G: Ohio SSBNs
Royal Navy (2025)
SSNs: Astute-class (6 of 7 in service)
- HMS Astute (commissioned 2010)
- HMS Ambush (2013)
- HMS Artful (2016)
- HMS Audacious (2020)
- HMS Anson (2022)
- HMS Agamemnon (Sep 2025)
- HMS Achilles (formerly Agincourt, the seventh and final boat) — expected in service by late 2026
SSBNs
- Vanguard-class (4 boats): HMS Vanguard, Victorious, Vigilant, Vengeance
- Dreadnought-class (4 boats in build): HMS Dreadnought, Valiant, Warspite under construction; HMS King George VI not yet started. Vanguard replacement begins early 2030s.
Reactor designer
Rolls-Royce Submarines (Derby, UK) designs UK naval reactors:
- PWR2 Core H: powers Vanguard and Astute classes
- PWR3: selected May 2011 for the Successor/Dreadnought class (in build)
French Navy (2025)
Aircraft carrier
- Charles de Gaulle (R91): commissioned 2001; the only non-US nuclear-powered carrier in service. Replacement PA-NG (Porte-Avions de Nouvelle Génération) planned for 2038.
SSBNs: Triomphant-class (4 boats)
- Form France’s SNLE oceanic strategic deterrent
- Force océanique stratégique continuously deploys at least one SSBN
SSNs: 6 boats total
- Rubis-class (legacy, retiring)
- Suffren/Barracuda-class: replacements
- Suffren (in service)
- Duguay-Trouin (in service / commissioning)
- Tourville (entered active duty 4 July 2025)
- De Grasse (sea trials)
Reactor designer
TechnicAtome (formerly Areva TA, partnered with Naval Group):
- K15: ~150 MWt reactor; ~32 shaft MW with electric drive and pumpjet; Triomphant SSBNs and Charles de Gaulle CVN
- K22: announced for next-gen French SSBN/CVN
Russian Navy (2025)
Submarines (~54 nuclear of 79 total submarines)
- SSBNs (~14):
- Borei/Borei-A class (8 boats including Knyaz Pozharsky commissioned 24 July 2025)
- Delta-III/IV (6 older boats, declining)
- SSN/SSGN:
- Yasen/Yasen-M class (5 accepted; latest Arkhangelsk, Dec 2024)
- Akula-class (residual, retiring)
- Project 949A Oscar-II SSGNs (being phased out by ~2035)
Surface (CGN)
- Kirov-class Pyotr Velikiy (active)
- Admiral Nakhimov (modernised, returning to service)
Reactor designer
OKBM Afrikantov (Nizhny Novgorod):
- OK-650: typical Russian naval submarine reactor (Borei, Yasen)
- KN-3 (older, Kirov class)
People’s Liberation Army Navy (PLAN, 2025)
Submarines (~32 nuclear estimate)
Mix:
- 9 Type 093/093A SSNs
- ~14 Type 093B (improved)
- 9 Type 094/094A SSBNs
- Type 096 SSBN in development
Specific class counts vary across sources (NTI, Army Recognition, Military Watch). Treat estimates as approximate.
Reactor designer
CSIC subsidiaries (China Shipbuilding Industry Corporation, now part of CSSC after 2019 merger): Chinese state-owned reactor design through multiple subsidiaries.
Indian Navy (2025-2026)
SSBNs
- Arihant (commissioned 2016) — first Indian-designed SSBN
- Arighaat (commissioned 29 Aug 2024)
- Aridhaman (final trials Dec 2025; commissioning expected 1H 2026)
- S4* (launched Oct 2024, sea trials underway, induction expected ~early 2027)
India’s strategic deterrent is built around the Arihant class. Reactor design is indigenous via DRDO + DAE collaboration, with Russian technical support historically.
Russian Atomflot (civilian icebreakers, 2025)
Operational fleet (8 ships)
For the first time in late 2025, all eight active nuclear icebreakers are deployed simultaneously:
Project 22220 (LK-60Ya, twin RITM-200 reactors, ~60 MW propulsion):
- Arktika (in service 2020)
- Sibir (2022)
- Ural (2022)
- Yakutia (2024)
- Chukotka (launched, completing)
- Leningrad and Stalingrad (laid down at Baltic Shipyard)
Older Arktika-class (twin-reactor, ~75,000 hp):
- Yamal
- 50 Let Pobedy
Taymyr-class (shallow-draft, single reactor, ~50,000 hp):
- Taymyr
- Vaygach
Project 10510 “Rossiya” (LK-110Ya / “Lider”)
- Under construction at Zvezda (Russian Far East)
- First RITM-400 reactor manufactured Sept 2025; second under completion
- Reported ~26.9% complete (Dec 2025)
- Delivery slipped to 2030 per First Deputy PM Manturov (May 2024)
- Supply-chain disruption when Ursa Major (carrying two reactor hatches) sank in western Mediterranean Dec 2024
Reactor designer
OKBM Afrikantov:
- RITM-200: each reactor 175 MWt / 55 MWe, ~110 MW total propulsion per Project 22220 icebreaker, 7-year refuel interval
- RITM-400: ~315 MWt for Project 10510 LK-110Ya
Reactor designers (consolidated)
| Nation | Designer | Notable reactors |
|---|---|---|
| US | Westinghouse / BWXT | A1B, A4W, S6G, S9G, S8G |
| UK | Rolls-Royce Submarines | PWR2, PWR3 |
| France | TechnicAtome | K15, K22 |
| Russia | OKBM Afrikantov | OK-650, KN-3, RITM-200, RITM-400 |
| China | CSIC subsidiaries | Various Chinese designs |
| India | DRDO + DAE | Arihant-class reactor |
Steam turbine downstream
All naval nuclear plants are pressurised water reactors. The reactor heats primary coolant water (under high pressure to prevent boiling), which transfers heat to a secondary loop in a steam generator. The secondary loop water boils to steam, which drives steam turbines for propulsion (and electrical generation).
This means every naval nuclear ship is, mechanically downstream of the reactor, a steam turbine ship. Steam turbine technology is conventional and shares engineering principles with the (now-rare) merchant marine steam turbine LNG carriers.
The propulsion-relevant difference between nuclear and conventional steam ships:
- Range: nuclear ships have effectively unlimited range (refuel reactor every 7-30 years depending on design)
- Refuelling logistics: no fuel oil bunkering needed
- Speed: not directly affected by nuclear power (gas turbines and diesels can match speed)
- Power: can sustain high power for extended periods without fuel concerns
Strategic position
Nuclear naval propulsion is justified for:
- Strategic submarines (SSBNs): must remain submerged for months on patrol; nuclear is the only practical option
- Attack submarines (SSNs): long-range deployment, sustained submerged operations
- Aircraft carriers (CVNs): sustained high-power operations, no fuel logistics constraint
- Specialty ice breakers: continuous high-power operations in remote regions
Nuclear is not used for:
- Merchant ships: dramatically more expensive and politically sensitive
- Smaller naval surface combatants (frigates, destroyers): gas turbine + diesel sufficient for typical missions
- Any application where capex/political/safety constraints rule out nuclear
Related Calculators
See also
References
- US Naval Vessel Register
- IISS Military Balance 2025
- Janes Fighting Ships
- NTI / James Martin Center
- Rolls-Royce Submarines public information
- Atomflot — Russian state nuclear icebreaker operator
- BIMCO Maritime Forecast