BOMB disposal experts were called to deal with an unexploded shell in Portslade.
The alarm was raised just before 7am after the explosive device was discovered at the Tarmac depot in Basin Road South. It is believed it was hauled up by a dredger.
The Royal Navy bomb squad arrived at just before 11am and police said they were preparing to carry out a controlled explosion.
A Sussex Police spokeswoman said: "Shortly before 7am on Thursday an unexploded shell was reported to have been found on industrial premises in Basin Road South, Portslade.
"It is believed it had been hauled up from the seabed by a dredger.
"A military Explosive Ordnance Disposal unit was sent to deal with the weapon by means of a controlled explosion.
No evacuation was necessary."
Details about the precise nature of the device are not yet available.
Tarmac declined to comment.
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