The 500 pound World War Two device was picked up during dredging work.
Warning After Rope Swing Death
The mother of a 16-year-old boy who accidentally hanged himself on a rope swing in a game which went wrong said today she hoped his death could act as a warning to other parents.
An inquest heard that Joshua Twigg was found unconscious next to the swing which was attached to a tree close to the family home in Tangley Walk, Havant, Hampshire, on May 23 last year.
His 18-year-old twin brothers, Ben and Daniel, found him on the ground and at first believed Joshua, who had been out walking his dogs, was playing a joke on them.
The Portsmouth hearing was told that the brothers attempted to revive Joshua and fetched stepfather Christopher Ferguson, who carried out mouth-to-mouth resuscitation until paramedics arrived.
Attempts by the medics to save Joshua, who had a younger brother called Sam, were unsuccessful and he was pronounced dead at hospital.
The inquest heard the cause of death was hanging.
Detective Constable Louise Daniels, of Hampshire police, told the hearing that local children were known to play a game of placing their heads inside a loop of the rope to see how long they could endure it.
She said that Ben Twigg had told his mother Rizi Matthew, 43, at the funeral that he had seen Joshua play this game before.
Ms Daniels said: "He had told her this information at Joshua's funeral, he hadn't wanted to tell anyone about this before because he felt he was to blame because he hadn't told her before.
"Joshua had said to Ben that he could go to sleep like this and Ben had told him not to be an idiot and it could go wrong.
"He (Joshua) laughed it off and said it was fun."
Ms Daniels added: "There was no indication Joshua was depressed or suicidal, Joshua was a happy young man with great plans for the future."
Recording a verdict of accident death, Portsmouth coroner David Horsley said: "Although we can't say exactly how it happened or what Joshua was really doing at the time, it was some kind of experiment or game that has gone wrong, he may have lost his footing, but when it has gone wrong, there's no way back.
"We can't stop children from swinging on trees, I could contact the council but they can't be there all the time. Swings are there for children to have a good time.
"As long as there are trees, there will be children putting up swings and people doing silly things, I just wish Joshua's death could put a stop to that."
Speaking after the inquest, Ms Matthew said that her son, who was studying catering, had just found his 'first love' and had applied for his first job at McDonald's which they found out he had got a few days after his death.
She said: "It was a brilliant time in his life, he had turned into a right nice guy. I just want people to know it was a privilege to be his mum."
She added: "I knew it was an accident, I knew he wouldn't do anything silly, he had too much to live for."
She said she hoped the death of her son "could be a warning to other parents about rope swings, even if it saves one other child".
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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