Mr Sunak said that defence manufacturer BAE Systems had been awarded a £4.2 billion ($4.9bn) contract to build five more Type 26 frigates for the Royal Navy, on top of the three already under construction.
The UK-pioneered Type 26 is an advanced warship with the primary purpose of anti-submarine warfare. It will protect the UK’s continuous nuclear deterrent and Carrier Strike Group.
The new generation of British frigates will strengthen the UK’s defences and sustain 4,000 UK jobs.
Construction of the eight frigates is expected to be completed by the mid-2030s and when the ships are ready, they will be sent all over the world.
“Russia’s actions put all of us at risk," he said.
“As we give the Ukrainian people the support they need, we are also harnessing the breadth and depth of UK expertise to protect ourselves and our allies.
“This includes building the next generation of British warships.”
The expansion of the programme to build the frigates follows the attacks on the Nord Stream gas pipelines, which have been blamed on the Kremlin.
Meanwhile, Mr Sunak again declined to commit to a promise from his predecessor, Liz Truss, to raise defence spending to 3 per cent of GDP, compared to the Nato minimum of 2.5 per cent, as he and Chancellor Jeremy Hunt seek to balance the books.
“We’ve got not just a current but a historic track record of being strong investors in defence and prioritising Nato,” Mr Sunak said onboard a plane to Bali.
“I think people can feel completely assured that we’re investing in our defences.
“In terms of what does weaken Putin, I mean what he’s going to see from me is unequivocal condemnation of his actions at the G20."
Mr Sunak also spoke of the UK’s “significant” financial and military assistance for Ukraine.
“I don’t think Putin or anyone else can look at that and say in any way that we’re weak,” he said.
Mr Sunak will use the G20 summit to reaffirm the UK’s support for Ukraine.
As chancellor, Mr Sunak committed £4.1bn in direct support to Ukraine, including £2.3bn in military aid.
He has now committed to matching that level of spending on military support next year.
Mr Sunak is also preparing with allies to confront Russia’s representative at the summit, which starts on Tuesday.