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While there is no official global classification, industry website and magazine Boat International describes one as "a luxury, privately-owned yacht that measures 24 metres or more in length, and is professionally crewed".

Eight crews, three 4x4 brigade response vehicles and a hydraulic aerial platform are in attendance, crewed by around 50 firefighters.

They were taking part in the first crewed test flight of the Starliner spacecraft, which was developed by aerospace company Boeing.

Dr McDowell suggested it could take many more years for Starship to be ready for a crewed mission to the moon, which could begin to be "very embarrassing thing for Nasa to navigate".

A ship the size of a football field, crewed by more than 50 engineers and technicians, cruises the oceans around Africa to keep the continent online.