London, Jun 27 (IANS): A massive new aircraft carrier -- the largest warship ever built for the Britain's Royal Navy -- on Monday took to the seas from a northeastern Scottish dockyard as it was set to undergo two years of trials.

The steel colossus, named HMS "Queen Elizabeth", which came with a staggering price tag of 3.5 billion pounds ($4.5 billion), slipped out of the Rosyth Dockyard, near Edinburgh, before attempting to squeeze out of the dockyard with only 36 cm to spare on either side, Efe news reported.

"If you look at all the premier nations around the world, why is it that every nation in the top tier is investing billions of dollars in aircraft carriers? The reason being is that they provide the government, very simply, with an incredibly flexible tool," said Captain Jerry Kyd, who already commanded the HMS "Ark Royal" and HMS "Illustrious".

"It's not just about war-fighting. This is about deterrence, coercion, signalling, proving a huge sea base for disaster relief, humanitarian assistance and defence engagement," Kyd added.

The 65,000-tonne behemoth has a crew of 700 -- which can be expanded to 1,000 -- and the capability to carry up to 36 multirole Lockheed Martin F-35B Lightning II stealth fighters.

After six weeks of trials in the North Sea, the carrier is set to return to Rosyth for a check-up before sailing to Portsmouth, its designated home port. It is scheduled to become operational in 2020, 11 years after its construction started.

Both ships have been the target of criticism because they were designed to be used with US-built F-35B short takeoff and vertical landing aircraft, the world's first supersonic STOVL stealth aircraft.

A second carrier, the future HMS "Prince of Wales", was ordered in 2008 and is also being built in Rosyth, with around 80 per cent of it said to be structurally complete.