The Royal Navy was today preparing to detonate a 2,000lb Second World War mine picked up at sea by a dredger.
The device was found eight nautical miles off the coast of Essex at 9am yesterday morning.
Karl Bigwood from the Walton and Frinton lifeboat crew described it as one of the largest the station had dealt with.
"There are lots of bombs out there but that was one of the largest, and to get stuck in a dredger's suction pipe is quite unusual.
"That size of bomb isn't normally around," he said.
A Maritime and Coastguard Agency spokeswoman said the Royal Navy planned to explode the mine by 10.30am today.
She said: "Thames Coastguard put an exclusion zone around the vessel of one nautical mile. They put a Royal Navy diving unit onboard yesterday morning and they are still onboard now.
"They are going to take the bomb off, put it on a flotation device, take it away from the dredger and detonate it."