"I was like, 'Holy heck, eh?'" Danny Vellow, who found the artillery shell, said.
The remains of the AE1, which vanished in 1914 with 35 crew on board, have been located near Papa New Guinea.
The battle began on July 1, 1916, and turned the tide for the Allies.
During the First World War, desperate women wrote to 'Fanny Deane', but she was not quite what she seemed.
'O Jesus make it stop!' wrote Siegfried Sassoon. On November 11th 1918, at 11am, it did – and Europe's 20-year peace began
Britain's government will pay off part of the nation's First World War debt as part of a redemption of bonds stretching as far back as the eighteenth century.