Britain will build new attack submarines, invest billions on nuclear warheads and move toward “war-fighting readiness,” Prime Minister Keir Starmer said, shortly before the publication of a landmark review of the future of the country’s military.

Starmer’s government said it would build “up to” 12 new attack submarines as part of its AUKUS partnership with the United States and Australia, replacing the country’s current class of seven subs from the late 2030s.

And he will launch a “historic renewal” of the UK’s nuclear deterrent backed by a £15 billion (A$31.3 billion) investment, Starmer said in a speech in Scotland on Monday.

The announcements came on the same day as the publication of the long-awaited UK Strategic Defence Review into Britain’s armed services, which outlined how the British military would pursue an “immediate” shift toward greater use of autonomy and AI in the wake of Ukraine’s experiences in its war with Russia.

“When we are being directly threatened by states with advanced military forces, the most effective way to deter them is to be ready, and frankly, to show them that we’re ready to deliver peace through strength,” Starmer said Monday.

But Starmer refused to set out the timeline for his pledge that Britain’s overall defence spending would hit 3 per cent of the UK’s gross domestic product (GDP). The uplift, announced earlier this year, is set to be reached by the end of the next parliament in 2034, but is dependent on economic conditions.

And the prime minister did not set out where the money to pay for the new weaponry will come from; he previously announced cuts to the UK’s aid budget to fund the uplift in defence spending, and he declined to rule out similar moves on Monday.

According to the 144-page review, units in future will be made up of only 20 per cent crewed vehicles, with the remainder of capabilities split between “reusable” platforms, like drones that survive repeated missions, and 40 per cent single-use weapons, like rockets or attack drones.

The Royal Navy is to “move toward a more powerful but cheaper and simpler fleet,” and the UK’s two aircraft carriers (the largest in Europe) will shift to being used as a base for European – rather than only British – aircraft and drones.

Meanwhile, under the waves, unmanned subs and sensors will police the North Atlantic against Russian military movements.

However, some such capabilities will require a decade of investment and development, Dr Marion Messmer, a senior research fellow at thinktank Chatham House told CNN.

That stretches far beyond the forecast of certain European countries that Russia could be ready to threaten European borders militarily six months to a few years after ending fighting with Ukraine.

Even so, the boosted investment in the UK’s nuclear capabilities as well as potential integration with European deterrence outlined in the document will strike a nerve with Moscow, she said.

The fiscal promise from the UK falls short of defence spending promises from some NATO countries, whose spending has been closely scrutinised by US President Donald Trump.

NATO’s Secretary General Mark Rutte said last month he “assumed” NATO members will agree on a defence spending target of 5 per cent at June’s NATO summit, a significant increase from the 2 per cent benchmark, which was agreed to in 2014.

The US’ defence expenditure sat at 3.38 per cent of GDP in 2024, making up some 64 per cent of total NATO expenditure.

Just weeks before NATO allies could agree on a significantly higher spending target, “it seems a little risky for the UK government to essentially have boxed itself in” to a 2.5 per cent-of-GDP spending cap, analyst Messmer told CNN.

The UK’s ambition to lead in NATO, doesn’t fit with spending in the middle of the pack among NATO allies, she said.

Countering the Russia threat

Russia’s invasion of Ukraine – and the subsequent pressure from Trump’s administration on European nations to boost their own military capabilities – has sparked a race among Europe’s key military powers to boost their readiness and counter the Russian threat should the White House pull its support for Kyiv.

The UK “cannot ignore the threat that Russia poses,” Starmer told the BBC on Monday. “Russia has shown in recent weeks that it’s not serious about peace, and we have to be ready.”

Starmer said Monday he intended to turn the UK into a “battle-ready, armor-clad nation with the strongest alliances, and the most advanced capabilities, equipped for the decades to come.”

Government MP and member of the British Parliament’s Defence Select Committee, Fred Thomas, told CNN that the review was a “bold plan,” and the first since the 1980s that argued for doing more, not less, with the UK’s military.

However, the British military of today is a long way from its Cold War ancestor. At under half the strength of the regular military in 1989, the British army is a shadow of its former self. In 1989, defence spending accounted for 4.1 percent of GDP.

“If you want to prepare for tomorrow’s war, you need to make sure you’re at least ready for today’s war. And we’re not ready for today’s war,” MP Thomas said.

The planners hope machines will make up for manpower.

As part of the UK military “fundamentally transforming how it works,” the review recommended enabling any sensor and weapon across the armed forces’ arsenal to work in tandem, using AI to predict threats and speed up decision-making.