Construction of the UK's four new nuclear submarines is to begin, after the government announced £1.3bn of new investment with defence firm BAE Systems.
The "Successor" is the proposed new generation of submarines to carry the UK's nuclear deterrent.
Defence Secretary Michael Fallon said the deal would secure thousands of highly-skilled jobs across the UK.
"This shows the government will never gamble with our national security."
The four new Successor submarines, which will carry Trident missiles, are to be built at BAE Systems' shipyard in Barrow-in-Furness.
The project will move into a new phase from next week, with manufacturing beginning on structural steel work for the first vessel.
The defence firm says they will enter service from the 2030s onwards and have a lifespan of at least 30 years.
The Ministry of Defence says several hundred suppliers are expected to be involved in the new programme at its peak, securing jobs from Scotland to the south of England.
Britain has four Vanguard class submarines that have been in operation since 1992, and had an intended service life of 25 years.
One is always deployed at sea, while another undergoes maintenance and two are in port or on training manoeuvres.
In July, MPs voted to renew Britain's ageing nuclear weapons system by 472 votes to 117.
The vote approved the manufacture of four replacement submarines at a current estimated cost of £31bn.
Labour was split over the issue with 140 of its 230 MPs going against leader Jeremy Corbyn and backing the motion.
Labour's policy is in flux amid continuing divisions at the top of the party, after endorsing Trident renewal at the last election but Mr Corbyn having been a lifelong opponent of nuclear weapons.
The government says the UK's independent nuclear deterrent is essential to national security.
Unveiling the new investment, Mr Fallon said Britain's ballistic missile submarines were used every day "to counter the most extreme threats".
"We cannot know what dangers we might face in the 2030s, 2040s and 2050s so we are acting now to replace them."
SNP MSP Bill Kidd said it was "wrong to pursue the renewal of such a morally objectionable weapons programme".
"We don't want weapons of mass destruction based here in Scotland just a few miles from our biggest city, and we should be leading the world in getting rid of the obscenity of nuclear weapons once and for all," he said.