Construction work will begin on the successor submarines that carry the controversial Trident missiles in Barrow-in-Furness.
Defence Secretary, Sir Michael Fallon announced £1.25 billion to begin the first building phase of the new fleet for the nuclear deterrent system.
The money for BAE Systems will be used to build the part of the submarine that controls the reactor as well as completing designs and investing in facilities at its Barrow-in-Furness yard.
Sir Michael, who made the announcement ahead of the Conservative party conference in Birmingham, said the submarines were the "ultimate guarantee of our nation's safety".
Renewal of the continuous-at-sea deterrent is predicted to cost £31 billion, with a £10 billion contingency fund also set aside.
The Scottish government is fiercely opposed to the "immoral" weapons system, but 140 Labour MPs voted with the Conservative government in Westminster to back renewing the deterrent in a Commons vote in July.
Labour leader Jeremy Corbyn voted against the plans and has previously said he would not push the nuclear button if he took the keys to No 10.
Work will begin on the first of the new submarines and will secure thousands of highly-skilled jobs in the UK and the North West.
"Britain's nuclear submarines are the ultimate guarantee of our nation's safety - we use them every day to deter the most extreme threats. We cannot know what new dangers we might face in the 2030s, 2040s and 2050s so we are acting now to replace them.
"A central part of this nation's defence, the Successor submarines, will protect each and every one of us, as well as future generations.