The British HMS Prince of Wales aircraft carrier broke down soon after leaving southern England's Portsmouth port, according to The Guardian.

The Royal Navy is currently carrying out "investigations into an emerging mechanical issue," a spokesperson told the newspaper on Sunday.

The 65,000-tonne warship was heading to the United States for a four-month deployment when it broke down. It currently remains in the south coast exercise area, close to the Isle of Wight, The Guardian reported.

According to the online publication of the Navy Lookout, divers have been inspecting it after the damage was reported to one of the propeller shafts of HMS Prince of Wales.

It was due to cross the Atlantic with a crew of 1,600 who were going to carry out training with the US military and the Royal Canadian Navy in a program with F-35B jets and uncrewed systems.

The vessel, which is the second most expensive military vehicle in the world and Nato’s flagship carrier, was out of order in 2020 for six months due to flooding of its engine room. 

The Guardian added that during the carrier's first two years in service, it reportedly spent fewer than 90 days at sea after springing leaks twice in five months.

Last year, the British Royal Navy submarines got engaged in what they described as a “race against the Russians” to recover the wreckage of an F-35 plane, worth 100 million sterling pounds (more than $134 million), equipped with “top-secret technology” from the bottom of the Mediterranean Sea, near the Egyptian Sinai. 

The Daily Mail newspaper reported that a British pilot was forced to eject from his F-35B Lightning II as it ditched into the sea soon after taking off on 'routine exercise' from the Navy's flagship aircraft carrier, HMS Queen Elizabeth. 

According to the sources, the crashed plane was one of eight British fast jets in this category on the British aircraft carrier, along with 10 American planes.