After nearly a decade of construction, Britain's biggest ever warship will set sail for the first time today - with the Russians watching - in a historic moment for the Royal Navy.

Weighing 65,000 tonnes and measuring 280-metres long, it is so large its captain yesterday described it as the UK's new 'sea base' - which will take the fight to any adversaries across the globe.

But before the £3.1billion aircraft carrier can start policing the seas, it has to successfully navigate out of its Scottish dockyard without clashing with its first enemy - a bridge.

All eyes today will be on Chief Petty Officer Andrew Vercoe as he steers HMS Queen Elizabeth out of the dock at Rosyth and into the North Sea in a nerve-racking ten-hour operation.

With the aid of 11 tug boats and two pilots on the shore, the state-of-the art new 'national symbol' will have to squeeze out of the basin with just 14 inches to spare on each side.

Then the 733-strong crew will have to wait for a low tide and the perfect wind conditions before it passes under three bridges in the River Forth in a process that has been simulated some 30 times.

As the carrier approaches Forth Bridge, which has stood between the dockyard and the open seas for 127 years, Commodore Jerry Kyd will get out a sextant navigation tool used in the 18th century.

Then, with the captain's approval, the ship - with its hi-tech radar atop its mast bent at 60 degrees - should, hopefully, sail under the bridge with just 2 metres to spare.