Outgoing British Prime Minister Keir Starmer unveiled a sweeping new defense investment plan Tuesday that will increase U.K. military spending by 27% in real terms by 2030, marking the largest expansion of Britain's armed forces since the end of the Cold War and positioning the country as one of Europe's dominant military powers.

The long-delayed Defense Investment Plan commits an additional £15 billion ($20 billion) in new funding over the next four years, bringing total British defense spending to £298 billion ($393 billion) through the end of the decade.

Starmer, who is expected to leave office next month after losing the support of Labour lawmakers, described the plan as a defining achievement of his premiership.

"This game-changing investment will strengthen our Armed Forces on land, at sea and in the air, ensuring our servicemen and women have the cutting-edge capabilities they need to deter evolving threats and keep the British people safe," Starmer said.

The plan raises Britain's annual defense budget to nearly £80 billion by 2029, representing about a 5% increase in yearly spending. According to the government, the increase puts Britain on course to meet NATO's target of spending 3.5% of gross domestic product on core defense by 2035, while total security spending would reach 4.2% of GDP.

Reuters reported the increase comes as European nations respond to pressure from President Donald Trump to shoulder a greater share of NATO's defense burden.

British officials said the investment makes the United Kingdom the third-largest defense spender among NATO's 32 members in cash terms and places it among Europe's top military powers.

A central focus of the blueprint is preparing Britain's military for the changing nature of modern warfare, particularly lessons learned from the conflicts in Ukraine and the Middle East.

More than £5 billion ($6.6 billion) will be invested in drones, autonomous weapons and unmanned systems over the next four years, representing the largest drone investment in British military history.

The Royal Navy will receive six new warships while developing a "Hybrid Fleet" that combines traditional vessels with autonomous surface and underwater drones. The Army will field new autonomous combat drones alongside Apache attack helicopters under Project NYX, while the Royal Air Force will develop autonomous fighter aircraft designed to fly alongside manned jets by 2030.

The investment plan also strengthens Britain's nuclear deterrent, funds development of a next-generation stealth fighter aircraft and establishes a £2.1 billion Defense Innovation Fund to accelerate military technology research.

NATO Secretary-General Mark Rutte welcomed the announcement, calling it "a good step towards reaching the 3.5% of GDP on defense agreed in The Hague last year."

Britain's largest defense contractor, BAE Systems, also praised the strategy.

"The government's commitment to increased defense spending is vital to sustaining the specialist skills across our industrial base critical to national security," BAE Systems Chief Executive Charles Woodburn said.

Despite the headline spending increase, critics argue the plan remains inadequate. Defense leaders had sought an additional £28 billion over four years, nearly double the amount Starmer approved.

Retired Royal Navy commander Tom Sharpe dismissed the blueprint as "cost-cutting by another name," arguing that equipment purchases will still be delayed while training, infrastructure maintenance and logistics could face reductions.

Starmer defended the funding, saying it is fully financed through reallocating spending from other government priorities, including postponing some road and energy projects.

"When the world is arming and aggression is rising, the best way to avoid war is to prepare for it," Starmer said. "The best way to defend is to deter — to have the strength to make your adversaries think again before they act."

The prime minister acknowledged that his likely successor, Andy Burnham, expected to take office later this month, would ultimately decide whether to expand the ambitious military modernization program further.