The mast has been fitted on the Royal Navy's new aircraft carrier HMS Queen Elizabeth, making it Britain's tallest warship.
From the tip of the newly-installed pole mast to the keel, the carrier now stands at 73 metres tall - taller than Tower Bridge or Nelson's Column.
With a draught of 10 metres it means the aircraft carrier - due to be officially named by the Queen at Rosyth, Scotland, on July 4 - will stand 63 metres above the waterline.
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But at that height, the ship is too tall to sail beneath either of the road or rail bridges over the Forth.
Engineers have created a solution by enabling the pole mast to be lowered until it is almost horizontal.