The carriers will be the Royal Navy's largest vessels
The Princess Royal has cut the first steel for Britain's biggest new warship to mark the start of construction work.
The Princess pushed the button to start the computer guided laser that cut the steel at the BVT shipyard in Govan.
The carrier is one of two ships being built as part of a £5bn order for the Royal Navy.
The work has secured thousands of jobs on the Clyde, though there are doubts about the yards' future when these ships are finished.
HMS Queen Elizabeth and the second ship, HMS Prince of Wales, will be the biggest ever to enter Royal Navy service.
The Govan yard is to fabricate much of the hull, the deck support and the propulsion system, with propellers weighing 33 tonnes each.
Work on the vessels will also take place at Portsmouth, Devonport and Tyneside.
They will then be assembled at Rosyth in Fife.
The vessels will be capable of carrying up to 40 aircraft and will be used for a wide range of tasks, including supporting peacekeeping operations and conflict prevention.
During the ceremony, First Sea Lord Admiral Sir Jonathon Band said: "After over 10 years of debate, uncertainty, planning, and frankly some insidious behaviour, I am delighted that the steel for the first of two ships is about to be cut."
"These ships are not just spare airfields, they are an instrument of national power. The 'big stick' which can be waved by the Government in areas of strategic interest to influence, coerce and deter."
HMS Queen Elizabeth will come into service in 2014, followed by the HMS Prince of Wales in 2016.
Each ship will be a similar size to the QE2 ocean liner, with a flight deck the size of three football pitches.
Kenny Carmichael, 29 years at Govan: "Shipbuilding's always been under threat"
The work represents job security through the recession for nearly 4,000 shipyard workers on the Clyde.
However, leaked documents from the yards' owners, BVT, showed a plan to close some yards in the UK after the carriers are complete.
The government has insisted the Scottish yards have enough work to secure their future for 15 years.
The steel was cut ahead of an announcement that the government is to launch a full-scale review of Britain's Armed Forces.
It is likely that the review will consider whether the two carriers are the right option for the future.
Questions have also been raised over whether the renewal of Britain's submarine-launched Trident nuclear deterrent should go ahead or whether a cheaper alternative should be found.
It is the first examination of how Britain's military is organized since 1998.
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