Bomb squad officers were called to carry out a controlled explosion on a shell found by a fellrunner.
The runner made the discovery over the bank holiday weekend in the Langsett area on the eastern edge of the Peak District.
He contacted Woodhead Mountain Rescue Team and gave them the location of what he believed was a mortar shell.
A team spokesperson said: “Two of our team members who have good knowledge in this area went to investigate and confirmed the fellrunner’s findings were correct and made contact with the Royal Logistic Corps bomb disposal team and South Yorkshire Police.
“With it being a bank holiday and very busy in the area, team members along with the Royal Logistic Corps bomb disposal and South Yorkshire Police needed to make the area safe and decided on a controlled explosion in the evening once most of the walkers visiting the area would have returned home.
“RLC confirmed that the shell was in fact a live high explosive left over from the shooting range that took place during the Second World War. The area was prepared for a controlled explosion of the shell resulting in quite a bang.”
The team said this kind of find is not uncommon in the area around Langsett Reservoir, west of Stocksbridge.
The spokesperson said: “If you do come across anything that does look suspicious, please don’t touch the device but mark the area if you can, phone the Police and give an accurate location of your find.”