The U.K. on Monday announced new plans to overhaul its defensive posture in the wake of Russian President Vladimir Putin’s invasion of Ukraine and potential challenges posed by President Donald Trump's threat to withdraw U.S. troops from the continent.

British Prime Minister Keir Starmer said he would bring his country to "war-fighting readiness" by investing dozens of billions of dollars in the building of 12 submarines, weapons and munitions manufacturing, AI and other tech, and most notably, a significant investment in nuclear deterrence.

The announcement came after a Strategic Defense Review by an external board found several areas in the U.K. that need to improve in order to effectively deter aggressors like Russia, as well as North Korea, Iran and China.

While the review heavily focused on changes that need to be made to the U.K.’s defense readiness, it also identified a need to bolster societal resilience and support.

"Our response cannot be confined to increasing defense spending," Starmer said in a statement from the report. "We also need to see the biggest shift in mindset in my lifetime: to put security and defense front and center—to make it the fundamental organizing principle of government."

The 144-page plan released by the British government on Monday laid out a new defense strategy to tackle threats "more serious and less predictable than at any time since the Cold War."

However, the biggest investment the U.K. revealed in its defense overhaul is a near $20.3 billion commitment to its nuclear warhead program in a move to expand its deterrence level, which, the report said, "sends the ultimate warning to anyone who seeks to do us harm."

The push has been described as a "NATO first" policy that will heavily focus on the immediate threats posed by Russia to the European continent. However, the plan is not a "NATO only" policy.

The U.K. plans to produce a new submarine every 18 months until it secures a fleet of up to 12 nuclear-powered attack submarines under the AUKUS program, which is a trilateral security partnership between Australia, the U.K. and the U.S. – which focuses on security and stability in the Indo-Pacific, particularly in the face of increased Chinese aggression in the region.

Defense Secretary John Healey said, "We are in a new era of threat, which demands a new era for U.K. defense."

Starmer ordered the review last summer, shortly after he secured the top job.

Security experts have warned that the threat Russia poses as it advances its war machine is assessed to be a generational threat, and one that will likely out-live the war in Ukraine or even a Putin presidency, and European nations have been scrambling to react to the new reality.

The re-election of Trump became another challenge European leaders have grappled with.

Though Trump pushed Nato leaders to increase their defense spending during his first term, most nations did not meet their GDP defense spending commitments under NATO until after Russia invaded Ukraine.

Now, just eight of the 32 NATO nations do not meet the 2% GDP spending commitments, while five nations, including the U.S. spend more than 3%.

NATO nations have increasingly called for an increase in defense spending and a push to be less dependent on the U.S.’s military industrial base.

While the U.K. has pledged to spend 2.5% of its GDP on defense by 2027, with an increase to 3% by 2030, Trump has called for NATO nations to spend 5% -- though the alliance has not yet agreed to such a plan, which the U.S. also falls short on, spending 3.38% according to figures released in 2024.

The U.K. is also looking to take more of a leadership role in NATO, particularly as the reliability of the U.S. has been called into question amid the war in Russia, and amid threats by Trump that he may drawdown troop numbers in Europe.