Britain will buy a new fleet of maritime patrol aircraft and create two new rapid-reaction "strike brigades" in a bid to ensure the armed forces are adequately equipped for the next five years, David Cameron will announce.
The Prime Minister will give details of an additional £12 billion of equipment spending when he sets out the Government's National Security Strategy and Strategic Defence and Security Review (SDSR) in the Commons.
He will also announce a 10-year extension to the operational lifespan of the RAF's Typhoon jets and upgrade work to give them ground attack capabilities - effectively adding two additional frontline squadrons.
Defence spending received a boost in the Budget, when George Osborne, under intense pressure from MPs and defence chiefs, declared that the UK would continue to meet a Nato target to devote at least 2% of national wealth to defence.
The Chancellor revealed yesterday that the purchase of new F35 Joint Strike Fighter aircraft for the Royal Navy's two new aircraft carriers would be accelerated - making 24 available by 2023 rather than the previously planned eight.
It has already been announced that the SAS and other special forces will get an extra £2 billion to improve their equipment, the RAF will double its number of drones, an extra £1.9 billion will be spent on cyber security and 1,900 new spies recruited.
The SDSR is also expected to reveal that the expected cost of renewing the UK's nuclear deterrent has risen - with the SNP warning against cutting the number of anti-submarine frigates to be built in Scotland to compensate.
Boeing has won an industry bidding war to provide nine aircraft to plug the gap left by the highly-criticised decision in the last review in 2010 to scrap a new generation of Nimrod aircraft.
Defence chiefs were forced to call in help from the France, the US and Canada to track a suspected Russian submarine off the coast of Scotland last year amid warnings the lack of patrols was allowing Moscow to spy on the UK's nuclear deterrent.
The American manufacturer had been considered the favourite as Royal Air Force crews are currently serving on P8 Poseidons with the US military to maintain skills.
Downing Street said the new 5,000-strong strike brigades would be equipped to deploy across the globe and would use the Army's new generation of Ajax armoured vehicles.
The Typhoons will now see service through to 2040 to answer RAF fears over the dwindling size of its resources - with the extended lifespan meaning there will be seven squadrons of around 12 aircraft.
As well as being enhanced to add ground attack capability to their aerial combat role, they wil be fitted with upgraded stealth radar equipment.
Mr Cameron, who will return to parliament later in the week to make the case for air strikes against Islamic State in Syria, said the strategy was based around "an understanding that we cannot choose between conventional defences against state-based threats and the need to counter threats that do not recognise national borders".
"Today we face both and we must respond to both," he wrote in the foreword to the SDSR.
"So, over the course of this Parliament, our priorities are to deter state-based threats, tackle terrorism, remain a world leader in cyber security and ensure we have the capability to respond rapidly to crises as they emerge.
"By sticking to our long-term economic plan, Britain has become the fastest growing major advanced economy in the world for the last two years. Our renewed economic security means we can afford to invest further in our national security.
"This is vital at a time when the threats to our country are growing.
"From the rise of Isil and greater instability in the Middle East, to the crisis in Ukraine, the threat of cyber attacks and the risk of pandemics, the world is more dangerous and uncertain today than five years ago."
Unions fear the strategy will include big cuts in the MoD's civilian workforce, with some suggesting that up to 12,000 staff could be affected.
Reviews are likely to be held on how to achieve the cuts, either through redundancies or privatisation, probably over five years.
"The Tories will claim they're protecting defence by not being seen to cut the military, but cuts on this scale to the civilian workforce would seriously undermine the support our armed forces get at home and on the frontline," said one union official.