Chancellor George Osborne has announced a £500 million investment for the Faslane naval base in Scotland, home of the UK's nuclear deterrent.
The Chancellor, who will visit HM Naval Base Clyde later, said the cash will fund the construction of sea walls, jetties and other projects as it gets ready to host the country's entire submarine fleet.
The 10-year programme beginning in 2017 will secure 6,700 jobs and create thousands more, Mr Osborne said.
But the SNP and Plaid Cymru, who want to scrap the Trident missile system, questioned the Chancellor's spending priorities.
Faslane, located around 40 miles from Glasgow, is home to missile-carrying Vanguard submarines and recently welcomed the third of seven planned Royal Navy Astute class attack submarines.
The Ministry of Defence is also expected to base the Successor class on the Clyde when they come into service from 2028, with crews and engineers potentially calling Faslane home until at least 2067.
The base's 6,700 military and civilian staff and contractors is expected to increase to about 8,200 by 2022.
The Chancellor said: "Today's announcement of more than £500 million demonstrates the UK Government's commitment to investing in the infrastructure and capability to ensure that Faslane remains the centre of UK submarine operations for the next generation.
"I'm proud to say that this Government continues to recognise that our brave armed forces across Britain have always been resolute in defence of liberty and the promotion of stability around the world.
"That's why I recently committed to meet the Nato pledge to spend 2% of our national income on defence every year of this decade. A strong and secure country is vital to both our prosperity and national security.
"There will be thousands more jobs right here in Faslane, as well as across the UK supply chain. Across Scotland, around 12,600 people work in defence and my defence spending commitments will secure these jobs and provide huge opportunities for defence, security and technology companies all over the UK."
The SNP's Westminster defence spokesman Brendan O'Hara said: "There is something fundamentally wrong with Westminster's values and priorities if the Chancellor thinks wasting billions on nuclear weapons is something to boast about when people are dying within our benefits system.
"And in defence terms too, at a time when Scotland's conventional defence footprint has never been smaller with major capability gaps, base closures and personnel numbers at an all-time low, it seems the Treasury apparently has a limitless pot to keep an unwanted and obscene arsenal of nuclear weapons afloat.
"Investment in Faslane is welcome - but it must be as a conventional base - and not more money spent on weapons of mass destruction."
Plaid Cymru leader Leanne Wood AM said: "As the Chancellor visits Faslane today to promote squandering millions more on the nuclear weapons industry, he does so against the backdrop of swingeing cuts to vital public services.
"This is further proof of George Osborne's warped priorities in thinking that a Cold War relic is more worthy of investment than our schools and hospitals.
"Plaid Cymru has long campaigned for Trident to be scrapped altogether. It is perverse to claim that billions should be spent on outdated weapons of mass destruction when so many are being hit by welfare sanctions and struggling with stagnant wages.
"With the parliamentary vote on Trident renewal expected next year, I hope the Labour Party will be able to rise above its current rifts and speak with one voice against attempts to commit the UK to a new generation of nuclear weapons."