By Mauro Orru

The U.K. government said it would commit 15 billion pounds ($19.89 billion) in additional funding for its armed forces, moving to buttress its defense industry in the face of what Prime Minister Keir Starmer called a more dangerous and volatile world.

The boost raises investments that the U.K. has earmarked for defense over the next four years to about 298 billion pounds, providing the country with additional firepower to shore up its military, replenish ammunition stockpiles and spend on drone technology.

Russia's invasion of Ukraine has upended the security architecture of Europe, prompting governments to review their spending priorities and redirect funding toward defense. Like other members of the North Atlantic Treaty Organization, the U.K. is seeking to improve the state of its armed forces and be in a better position to fend off potential threats.

"The world is a more dangerous and volatile place, so it is only right we are boosting the number of troops on the ground, rebuilding ammunition stockpiles and investing in cutting edge technology to ensure we outpace our adversaries for generations to come," Starmer said in a speech at the headquarters of British drone company Malloy Aeronautics.

The announcement comes weeks after John Healey quit as defense secretary in protest over what he said was the government's refusal to materially increase military spending. Since then, Starmer said he would step down as prime minister following a rebellion in his Labour Party, clearing the way for Andy Burnham, a left-wing former mayor, to likely become the country's sixth prime minister in seven years.

Starmer said Tuesday that the government had managed to boost defense investments by reallocating spending across government departments, meaning that some infrastructure and energy projects would no longer go ahead as planned.

London plans to spend over 63 billion  pounds to strengthen its  nuclear deterrent, fund submarines and a new warhead as well as purchase 12 F-35A fighter jets. It will also channel 11 billion pounds into a mix of long-range weapons, cruise missiles and munitions production, and over 5 billion pounds on drones and uncrewed ground vehicles.

Modern warfare in Ukraine and the Middle East showed that nations under attack and those in the vicinity are vulnerable to aerial threats from drones, injecting renewed impetus on governments to invest in unmanned aerial vehicles and drone technology. Earlier this month, French carmaker Renault and aerospace-and-defense company Thales agreed to work together to make drone munitions at scale.

After the 15 billion-pound boost, defense funding in the U.K. is set to climb to almost 80 billion pounds a year by 2029 from 54 billion pounds under the previous administration, according to government projections, boosting defense spending to 2.7% of gross domestic product from 2.3% in 2024 to what treasury chief Rachel Reeves said would be the highest level since the Cold War.

President Trump has demanded that European nations spend more on defense, often calling on governments on the other side of the Atlantic to raise their military-spending targets to around 5% of GDP.

NATO allies made commitments to spend 5% of GDP annually on core defense like military hardware as well as cyber defense, protecting critical infrastructure, civil preparedness and other security measures by 2035. Spending for core defense alone should hit 3.5%. The U.K. said it was on track to meet NATO's defense spending targets by then.

"This extra money and these choices send a clear signal to our allies and our adversaries alike: Britain is stepping up on security," Defense Secretary Dan Jarvis said.

Write to Mauro Orru at mauro.orru@wsj.com