Britain urgently needs to bolster its defences in the face of a growing threat from Russia, MPs have warned.
The Commons Defence Committee pointed out that while Russia could deploy 150,000 troops in 72 hours, it would take Nato six months to match that.
Defence capabilities abandoned after the Cold War need to be rebuilt with more aircraft, warships, tanks and missiles to deter further aggression by Russian president Vladimir Putin, the committee said.
With Russian submarines being spotted off the coast of Scotland, the committee said the lack of a maritime patrol aircraft, following the decision to scrap Nimrod, had opened up a "crucial gap" in UK defences.
It is also essential that the UK does not drop below its Nato commitment to spend at least 2% of the country's GDP on defence, the committee said, as doing so would risk undermining the Western alliance when "Putin's Russia will be looking very carefully for signs of weakness in Nato."
With defence spending set to drop below 2% of GDP after 2015-16 on current plans, the findings will add to the pressure on David Cameron to declare his commitment to the Nato target.
The requirements are many, including maritime surveillance, nuclear, biological, chemical and radiological warfare training, developing a ballistic missile defence capability, an enhanced Navy and Air Force, a comprehensive carrier strike capability, and full manoeuvre warfare capacity.
In its report, the committee said the world was "more dangerous and unstable" than at any time since the end of the Cold War, with an advanced military state challenging the borders of European nations for the first time in 20 years.
Criticisms of UK defences by the Commons Defence Committee:
The alliance's new very high readiness joint taskforce - capable of deploying 5,500 troops in 48 hours - will not be ready until 2016
The Royal Navy's fleet of frigates and destroyers has been reduced from 50 in 1990 to just 19
The RAF had been cut from 33 squadrons to seven, making it increasingly difficult to mobilise "critical mass" in the air.
Defence Secretary Michael Fallon dismissed the committee's finding that the UK's defence capabilities needed to be rebuilt as "nonsense".
"The UK has the second largest defence budget in Nato and the largest in the EU," he said. "We are the US's largest partner in the coalition air effort against Isil (Islamic State) - bearing more of the load in terms of strikes in Iraq than we played in either of the Gulf wars."