A Royal Navy aircraft carrier which was supposed to lead the largest NATO exercise since the Cold War is instead heading to Rosyth for repairs.

The fleet flagship HMS Queen Elizabeth had been expected to depart from Portsmouth Naval Base for Exercise Steadfast Defender involving more than 40 vessels off the coast of Norway, but final checks found an "issue" with the starboard propeller coupling and it is now destined for the Fife dockyard instead.

It's been replaced in the NATO exercise by Rosyth-built HMS Prince of Wales, which itself underwent months of repairs and upgrading work at the Babcock shipyard, before finally returning to Portsmouth in July last year.

Announcing the change of plans, Fleet Commander Vice Admiral Andrew Burns said: "Routine pre-sailing checks identified an issue with a coupling on HMS Queen Elizabeth's starboard propeller shaft.

"HMS Prince of Wales will take her place on NATO duties and will set sail for Exercise Steadfast Defender as soon as possible."

HMS Prince of Wales set sail today (Monday, February 12), a day later than had previously been scheduled.

Dunfermline Press: Crowds gathered in Portsmouth as HMS Prince of Wales left port for the NATO exercise off Norway. Crowds gathered in Portsmouth as HMS Prince of Wales left port for the NATO exercise off Norway. (Image: Gareth Fuller/PA Wire)

A Royal Navy spokesman said: "On completion of initial investigations, HMS Queen Elizabeth will sail for Rosyth in Scotland so any necessary repairs can be carried out in due course.

"The cause of the issue with HMS Queen Elizabeth is wear and tear of her starboard propeller shaft coupling."

Eighteen months ago, HMS Prince of Wales broke down as it was heading to a diplomatic mission to carry out exercises with the US Navy, Royal Canadian Navy and the US Marine Corps.

The carrier came to a halt off the Isle of Wight and was brought under tow back into harbour for the problem to be identified.

Inspections by divers and engineers found the carrier's 33-ton starboard propeller – the same weight as 30 Ford Fiesta cars – had malfunctioned, with a coupling holding it in place breaking.

An MoD spokesman said the issue on HMS Queen Elizabeth was "separate and not linked" to the earlier defect on its sister ship.

He said: "The issue identified is with the ship's shaft couplings. The ship's propeller shafts are too big to be made from a single piece of metal, so each shaft is made from three sections, which are connected using shaft couplings, which bind the shaft sections together."

HMS Prince of Wales was taken to the Babcock shipyard in Rosyth where it was built to undergo repairs to a propeller shaft, which took nine months to complete.

On that occasion, HMS Queen Elizabeth acted as the replacement for its sister ship on the US deployment.