Harrier jump jets, the Navy's flagship HMS Ark Royal and planned Nimrod spy planes have been axed and 42,000 jobs in the forces and MoD will go by 2015, the PM has said.
Unveiling the strategic defence review, David Cameron said defence spending would fall by 8% over four years.
BBC News website readers have been giving their reaction to the review.
Harry Dean, Leicester
Harry served for 30 years in the Royal Artillery. He now runs an organisation called Gemini which helps those leaving the military make the transition to civilian life.
"As a politician, Cameron talks well. I can see the benefits of going forward with technology, but I really can't see the benefits of reducing actual bodies. The numbers of personnel fit to fight is already too low.
I appreciate Afghanistan is funded from a separate pot, but we would struggle to deploy anywhere else. There is also bound to be an impact on the morale of those serving.
There will be questions over whether this government really cares about the armed forces. I think the troops in Afghanistan will be supported, but I'm worried about what we can do elsewhere.
As far as the personnel cuts go, across the board the Army comes out of it quite well in comparison to the RAF and the Navy, but 7,000 is still too many.
I think the defence review should have come outside the Spending Review and it should have lasted longer.
Our organisation, Gemini, is about helping those that leave the forces, but we need to ensure we have enough people to carry out the operational duties that are needed without over stretching either them or their families."
Gideon Jenkins, Caerphilly
Gideon was a warrant officer first class in the Royal Electrical and Mechanical Engineers. His last job was the trial and development of main battle tanks for army deployment in Iraq and Afghanistan.
"There are 80,000 civil servants working with the armed forces - that's another army! You have to consider the long-term implications of paying their wages, pensions; that money could be put into other government departments.
The government is right to reduce the number of tanks. But how many main battle tanks (MBTs) have we got in Afghanistan? Answer - none. The reason is they do not work in mountains, marsh land is too soft for them so they sink. MBTs came in to cope with trench warfare, it has long since gone and so should they.
As for the Ark Royal, it's no good if you're deploying the army inland. Conflict zones are often too far for the planes to fly to and the pilots would need to fly tactically just to get to the threat.
Today we're dealing with small terrorist groups and insurgents popping up anywhere and everywhere so we need to have equipment to deal with them quickly. We need helicopters, 8-wheeled vehicles; fast, mobile equipment.
The threat we're facing is changing; now it's cyber threats. The US is ploughing billions into it, that's what we should be focusing on, that's the real threat."
Bob Spinner, Lincoln
Bob served in the RAF for 34 years as a personnel administrator on the ground.
"I don't see it as a strategy review, I see it as a disarmament review. Strategy is the art of war but they're cutting personnel, the Ark Royal is being cut, the Harrier jump jet is being cut.
I see this as the slow degradation of our defence. People have already left the forces and the role of the armed forces has already changed.
Cameron is saying 'don't worry' but we're already over stretched. We are at a point where my colleagues in the blue suit would not have sufficient numbers to fill Wembley Stadium.
I have always believed that we should retain sufficient weaponry to defend the UK, but at this rate we're not going to have anyone to operate it.
People are stretched already, it's a thankless job as it is and we're about to lose more jobs. How can there possibly be more defence cuts?"
Bill Paynter, Silsoe
Bill served in the Territorial Army from 1962 until 1999.
"I don't like to see so many reductions in the Army - it takes away the flexibility and balance of the forces. It's just about financial saving and doesn't help the morale of soldiers on the ground and it may depress the numbers of people wanting to stay in the armed forces.
The RAF does need heavy cuts. I would also have preferred to see the Tornado go instead of the Harrier, which we can still use away from ships. We do still have the Typhoon which is a more modern aircraft.
The navy is already too small and it shouldn't have been touched at all. The RAF is twice the size of the navy, so the navy is bearing a disproportionate size of the cuts.
There is a need to cut the heavy armoured forces, but if we are cutting the number of tanks in the regular army then we need to keep those we have in the reserves just in case the need arises.
We have got a spending problem and there is over budgeting at the MoD, so we need to make the best of what we've got, but I think the review makes co-ordination between forces more difficult as everything is being pared back, and that will also mean less intelligence capability at HQ."
Christopher Harress, Edinburgh, UK
Christopher served in the Royal Navy for four years and in the Royal Naval Reserves for two years.
"Once again it appears the government are planning too far ahead when global security is ever changing.
The Falklands War spawned these two aircraft carriers but they are not necessarily needed 28 years later. New submarine-hunting frigates for the Cold War came into service in 1990 just as it ended. Armoured vehicles for Ireland arrived just when the Irish conflict was becoming less volatile, then they were used in Afghanistan.
It seems we have all the right equipment for all the wrong conflicts and this overplanning is not only costing billions of pounds but also costing many lives.
A pool of money that can meet the demands of the ever changing global military environment may be a solution, but Liam Fox making predictions for the next 30 to 40 years is naive and shows a lack of hindsight.
I would like to see how Britain's armed forces perform in the next five years, but in my experience we were too big and too wasteful. If David Cameron seeks to form a smaller, sleeker and more professional military then I'm all for it, provided we don't commit on the same scale we have done in the past."
Keith Spain, Gillingham
Keith served in the Royal Navy for four years on board HMS Illustrious.
"My concern as an ex-military man is that the changes Cameron is talking about don't involve the lads in Afghanistan.
In real terms a reduction in personnel means people will spend less time at home. The turnaround time is already very quick for people under such heavy stress in battle situations and decreasing numbers will reduce their recovery time.
It's also strange to see the Ark Royal go. It's the flagship of the navy and it's especially strange to see that decision taken when it's the newest of the three aircraft carriers.
There is a lot of wastage at the MoD - inflated prices and unwise spends. I think a decrease in military personnel is an easy cut, rather than sorting out the costly problems at the root.
I also don't understand Mr Cameron's haste, I guess it's because they need to cut deficits quickly. I just hope the higher level military have got it right and it's not the guys on the ground who will suffer."
Mark Taylor, Ellesmere Port
Mark served for ten years in the Royal Navy and is a veteran of the Falklands conflict.
"I cannot believe that Ark Royal is being decommissioned. I don't understand why they're getting rid of the younger of the three aircraft carriers.
First of all we know only too well the importance of air power at sea, whether aircraft are deployed for ground attack, land operations or combat air patrol.
The versatility of a carrier should not be underestimated and in these dangerous times we could leave ourselves vulnerable.
A 10 year gap with no fast jet capability at sea is too long to wait."