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Lifeboat crews from Sheerness had to rescue four people trapped at the historic Grain gun tower.
The RNLI lifeboat was launched just before 7am on Saturday, having been called out by the UK Coastguard.
Four people had reportedly been trapped in the gun tower throughout the night.
Vic Booth, Sheerness' RNLI spokesman, said: "The four young men made their way across the mud to the lifeboat and were helped onboard.
"All four, who were unharmed apart from being very cold, were then taken to the all tide landing at Queenborough and passed into the care of the Sheppey Coastguard Rescue Team."
Lifeboat crews were back from the Medway Estuary tower by 7.30am.