Boris Johnson has launched what is described as the deepest review of British foreign, defence and security policy in 30 years, stating "as the world changes we must move with it".
Downing Street says the integrated review will be Government-wide, going beyond the parameters of a traditional strategic defence and security review (SDSR) by looking at the “totality of opportunities and challenges” the UK faces.
They continued, stating it will be the largest review of its kind "since the end of the Cold War", repeating the promise made by the Prime Minister earlier this month.
The review will examine defence, foreign and security policy, threats of the next decade, relationships with allies and changing strategy on the international stage.
Both the procurement process used by the Armed Forces and its strength in the face of hostility will be focus points.
Mr Johnson's chief adviser Dominic Cummings has been a noted critic of the Ministry of Defence's (MOD) spending record, particularly on large-scale equipment programmes.
In a blog post, he said the UK's two aircraft carriers, which cost a combined £6.2 billion, could not be used against a "serious enemy".
The aim of the integrated review is to find a way for the government to be "structured, equipped and mobilised" to meet "the totality of global opportunities and challenges", Downing Street said.
The Government said the review will aim to create a more coherent and strategic approach to UK overseas activity while continuing to commit 2% of GDP to defence and 0.7% on international aid.
"I am determined to lead a Government that delivers for our people - both at home and abroad," the Prime Minister said.
"The UK’s institutions, expertise, leadership and values are renowned around the world.
"We cannot rest on our laurels. We must do more to adapt. We will be judged by how we respond to the opportunities ahead."
"As the world changes, we must move with it – harnessing new technologies and ways of thinking to ensure British foreign policy is rooted firmly in our national interests, now and in the decades ahead."
The integrated review will report to the Prime Minister, who will be supported by a cross-Whitehall team in the Cabinet Office and a small team in Downing Street - comprised of experts from inside and outside the Civil Service.
Departments across Whitehall will contribute to the review, including the MOD. Decisions will be made by the National Security Council, chaired by Mr Johnson.
Conclusions are expected by the end of the year, in line with the Comprehensive Spending Review, though it will take several years to implement the decisions made.
Watch: The Prime Minister promises the 'deepest' defence review since the Cold War, while speaking to the House of Commons earlier this month.
The chairman of the Commons' Defence Select Committee, Tobias Ellwood, said the review was "exciting" and "long overdue" and was a chance to understand "what role we want to play on the international stage and then, I hope, invest in our defence posture so we can make our mark.
"The character of conflict is changing," he said.
"If we want to have that tier one, day one capability, then we have to invest more.
"That means looking more at 3% than 2% [of GDP spent on defence] by the end of the parliament.
Mr Ellwood suggested there are areas where the MOD could be doing better to save money.
"I think there are some savings to be made," he said.
"It's important that the MOD puts its hands up and says 'We can do things better'."
The chairman of the Commons foreign affairs committee, Tom Tugendhat, told BBC Radio 4’s Today programme: "This is really the first serious defence review in 10 years. Its time really has come.
Asked about reports that the Prime Minister is considering cutting the Army but increasing defence spending, Mr Tugendhat said: "I want this to be foreign policy-led, so let’s see what the foreign policy aims that the Government sets out are.
"Once they have set out that aim, let’s look at the tools you need to achieve it.
"And I don’t know whether those tools are going to be more ships, more men, more aircraft. But let’s have a look at it properly and strategically."
Cover image: Royal Navy.