Article
Please read https://www.yahoo.com/news/world/articles/navy-entire-fleet-submarines-while-131000399.html of June 7, 2026, first.
Pete Comments
The UK Royal Navy (RN) is again suffering, politicly embarrassing, defensively dangerous, nuclear attack submarine (SSN) unavailability. This means all five Astute-class SSN's (HMS Astute, Ambush, Artful, Audacious and Anson) are unavailable, awaiting maintenance and repairs. The sixth (HMS Agamemnon) commissioned September 2025, is not yet ready to deploy. Last of class, HMS Achilles, is due to be commissioned sometime in 2028-29.
Constant checking by the RN detects a fault familiar to the RN. That is weakened or frayed piping that works with each Astute's PWR2 Reactor. Hot Pressurised water/steam can stress the piping over time. Minute piping holes may cause a release of low level radioactive water. If left undetected or unrepaired this may cause the piping to burst.
While the piping contains hot water/steam this is not as hot as the fissioning U235 in the core of the reactor. However slowdowns or interruptions to the water/steam may cause an increase in temperature within the reactor which causes or triggers an automatic emergency shutdown of reactor function (called a reactor "trip" or "Scram").
So it is important that piping is intact and working efficiently. For the Astute's PWR2 reactor this is essential.
Put another way once the pipes split there can be loss of water based coolant demanding shutdown of the sub's reactor (at sea and especially in port). Any risk of release of coolant to civilian populated areas is, according to the UK Ministry of Defence (MoD), negligible, nothing to worry about. Although the dangers of this piping-to-reactor-risk has been examined and debated for many years. See this semi-paywalled 2011 Guardian article https://www.theguardian.com/world/2011/mar/10/royal-navy-nuclear-submarine-reactor-flaws . Failing that see this 2014 BBC article https://www.bbc.com/news/uk-politics-26463923 ).
This problem was earlier observed with the UK's post-collision HMS Vanguard nuclear missile submarine (SSBN).
Nuclear sub owning governments routinely assure publics how safe nuclear sub operations are. Here is the very long list of submarine mishaps, including an explosion and nuclear submarine collisions, since the year 2000.
During the Astute-classes availability failure the RN must rely on USN or French Navy SSNs to perform the highest priority tasks of escorting UK Vanguard-class SSBNs in and out of the UK SSBN base. The base is HMNB Clyde, near Glasgow, Scotland.
The mainly UK designed submarines, known as SSN-AUKUS, that Australia will buy/build, later than we're paying for, around 2045, will be heavily based on the Astutes. The PWR3+ reactor powering SSN-AUKUSes will owe much to the troubled PWR2 design.


