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A small lifeboat was engulfed with waves and came close to being thrown onto rocks by savage seas.
Three crew members had to go chest deep into the water to hold the RHIB (rigid-hulled inflatable boat) away from the rocks.
Walmer RNLI were called out at 10.35am on Sunday to aid three people cut off by the rising tide at Ness Point near St Margaret's Bay.
The Class D inshore lifeboat Duggie Robard II was launched after a request by HM Coastguard.
The casualties were found on an outcrop a couple of metres above the water.
Two crew from the Walmer station’s larger Class B Atlantic 85 Donald McLauchlan transferred to the smaller craft for extra manpower.
Members struggled with horrendous conditions with sea swells coming from different angles and the rocks hidden beneath Duggie Robard II.
Two went to the casualties handing them lifejackets, masks and gloves.
Two others stayed with the helm as the sea lifted the boat up and threatened to throw it onto the chalk rocks behind.
The first casualty was successfully transferred but seconds later a wave crashed over the bow of the boat and engulfed it.
After the transfer of the third casualty the whole mattress of the vessel had disappeared due to the water on board.
The additional weight caused the vessel to start drifting and the crew battled to keep it pointed to sea.
One crew member reboarded Duggie Rodbard II and Donald McLauchlan recovered the remaining crew from the sea.
Near the shore, Langdon and Deal Mobile Coastguard teams with dry suits and lines helped recover the casualties who were brought ashore.
Two or three further swells broke over the stern and swamped the boat again.
RNLI helmsman Dan Sinclair said: "This was the most challenging shout I have been involved in - mentally more than physically as I was the person making the decisions.
"Without the assistance of our Atlantic crew this rescue would not have been possible.
"I am so proud of all of the crew today performing outstandingly in very challenging conditions.
"Each and every one of them played a vital role in getting the casualties home safe."