David Cameron will "make the case" for Britain to join its allies in targeting the so-called Islamic State militant group in Syria later this week, he has announced.
Updating the House of Commons on Britain's security and defence activities, the Prime Minister said he would go before MPs on Thursday to try to encourage his colleagues to support extending action from its current focus of Iraq.
ITV News deputy political editor Chris Ship reports:
He argued they had to recognise their enemy did not respect the same national borders.
Mr Cameron's speech comes after he flew to Paris to meet Francois Hollande discussing how they can work together to defeat Islamic State.
He announced the government would invest £178 billion in buying and maintaining equipment over the next decade.
However, this will come at a cost, with hundreds of jobs at civilian jobs at risk and the cost of Trident spiralling to above £40bn.
The investment includes:
Increase size of deployable armed forces to 50,000 by 2025
Two new 'strike brigades' - forces of up to 5,000 rapid response personnel each
Two additional Typhoon squadrons
Additional squadron of F35 Lightning Combat aircraft
Replace four ballistic missile submarines
Nine new maritime patrol aircraft, to be based at RAF Lossiemouth in Scotland
13 new frigates - including eight type 26 anti-submarine warfare vessels
Two new offshore patrol vessels
By 2030s, increase total number of Royal Navy frigates and destroyers
This investment is "vital" at a time when threats are growing, he said - and told MPs that none of the items mentioned were "optional extras".
Mr Cameron also detailed a major new contingency plan to deal with potential terrorist attacks, including up to 10,000 military personnel will be made available to support police in dealing with Paris-style attacks.
New, British-designed surveillance drones will also fly near the edge of the atmosphere to provide intelligence, he added.
But the investment does come at a cost.
More than 16,000 civilian roles are at risk in the Ministry of Defence amid £11bn of cuts within the department.
Meanwhile, the cost of Trident has risen from an estimated £25bn to £31bn, with an extra £10bn of contingency put aside.
ITV News political correspondent Carl Dinnen explains: