The 500 pound World War Two device was picked up during dredging work.
HMS Liverpool Decommissioned Today
HMS Liverpool is being decommissioned at Portsmouth Naval Base today.
The ageing Type 42 destroyer has steamed more than 921,700 nautical miles in 30 years, protecting the nation's interests across the globe.
She is being taken out of service as the Type 42s make way for the hi-tech replacement Type 45 destroyers.
Built by Cammell Laird at Birkenhead, HMS Liverpool was launched in 1980. After an accelerated trials period she sailed for the South Atlantic in June 1982. Though she did not see active service in the Falklands conflict she remained on station for the next six months.
In 2003 she sailed from the UK as part of a task group intending to take part in exercises in the Far East but instead the group was diverted to the Persian Gulf to take part in the Iraq War. Throughout the conflict Liverpool acted as escort to the aircraft carrier HMS Ark Royal.
Liverpool was again involved in a major operation last year, playing a significant role in the blockade off Libya during the country's civil war.
While engaged in surveillance operations during the mission Liverpool came under fire from a shore battery, making her the first Royal Navy warship to be deliberately targeted since the Falklands conflict. During seven months off Libya Liverpool fired more than 200 rounds from her main gun.
Since returning from Libya in November Liverpool and her 260 crew have remained at the forefront of UK defence. Last month she was activated to intercept a Russian Naval task group - which had passed through the Strait of Gibraltar - to see them safely past UK waters into the North Sea.
She then paid an emotional final visit to her namesake city and will make her last entry into Portsmouth having just taken part in cold weather exercises close to the Arctic Circle.
Her Commanding Officer, Commander Colin Williams, said:
"In the 18 months since I assumed command, HMS Liverpool and her ship's company have achieved some of the highest accolades a Royal Navy warship could hope for. We have grown and faced challenges together, from operations off Libya to exercises in Norway, including sea training, high seas firings and escorting a Russian task group. We have achieved a great deal in a short time, and continued the long-standing, hard working tradition of the Type 42 destroyer.
"Every ship has a life span, and it is with great pride that we make way for the new Type 45 destroyers, and the enhanced capability they bring to today's Royal Navy. HMS Liverpool has served her country and ship's companies well to the end, and all should be rightly proud to have served in her. We bring her home as a ship at the top of her game, a fitting farewell to 30 years of dedicated service."
640 men were killed when the South African troop carrier was hit by a cargo ship in 1917.
The 79-year-old man suffered a serious head injury in the Cranmer Road car park in Winton.
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