Engineers have been carrying out inspections of the aircraft carrier HMS Prince of Wales after it broke down on its way to the US.
The warship left Portsmouth Naval Base on Saturday before an "emerging mechanical issue" occurred off the south-east coast of the Isle of Wight.
It may miss important flight trials with F-35B Lightning jets off the US coast after it suffered a propeller shaft malfunction, the Royal Navy has confirmed.
The departure of the Nato flagship had already been delayed from Friday because of a technical problem, although it is not known if the incidents were related.
Shortly after the 65,000-tonned ship sailed on Saturday, a mechanical fault was discovered with the starboard shaft.
The carrier languished about five miles from Shanklin before it limped back to Stokes Bay at Gosport, Hampshire, travelling at a rate of four knots accompanied by tugs for the return journey to calmer waters.
It is understood that anchoring at the sheltered bay near Portsmouth will allow divers to assess the damaged shaft.
Rear Admiral Steve Moorhouse, director of Force Generation, who is responsible for making sure Royal Navy ships are ready to deploy, said in a video statement: "I've been to the ship today to see for myself what the issue is and how we in the Royal Navy can work together to make sure the ship can successfully return to her tasking.
"After the initial assessment, it's likely that the fault will require repairs which may impact the ship's programme.
"The ship is now moving to a more sheltered anchorage for further inspection and then we'll be able to provide further comment on the nature of the issue and the impact to her current schedule.
"We've reacted quickly to the emergent defect and are working closely with industry partners to resolve this as soon as we can.
"Rest assured, the Royal Navy continues to meet its commitments to deliver operations and to keep the UK, our partners and allies safe."
The carrier had been given a colourful send-off as it departed on Saturday afternoon and passed thousands of music-lovers at the Victorious Festival on Southsea Common in Portsmouth.
Pop favourites Sugababes were in the middle of their set when the giant ship sailed past with the crew lining the flight deck to get a view of the festival.
The Nato flagship was sailing to undertake training exercises with the US Navy, the Royal Canadian Navy and the US Marine Corps.
The programme was expected to include exercises with the F-35B Lightning jets.