Submarine plans
The Astute class is the Royal Navy's current fleet of attack submarines, which have nuclear-powered engines and are armed with conventional torpedoes and missiles.
As well as protecting maritime task groups and gathering intelligence, they protect the Vanguard class of submarines that carry the UK's Trident nuclear missiles.
The sixth submarine in the current Astute series was launched last October, with the seventh, the final one in the series, currently under construction.
The next generation of attack submarines that will replace them, SSN-AUKUS, have been developed with the Australian Navy under a deal announced in 2021 under the previous Conservative government.
The Ministry of Defence (MoD) said it expected the rollout of the new generation would see a submarine built every 18 months.
It added the construction programme would see a "major expansion of industrial capability" at BAE Systems' shipbuilding site in Barrow-in-Furness, Cumbria, as well as the Derby site of Rolls-Royce, which makes nuclear reactors.
Meanwhile work on modernising the warheads carried by Trident missiles is already under way.
The £15bn investment into the warhead programme will back the government's commitments to maintain the continuous-at-sea nuclear deterrent.
In his announcement on Monday, Sir Keir is to repeat a Labour manifesto commitment to deliver the Dreadnought class of nuclear-armed submarines, which are due to replace the ageing Vanguard fleet from the early 2030s onwards.
The MoD's Defence Nuclear Enterprise accounts for 20% of its budget and includes the cost of building four Dreadnought class submarines.
