Navy bomb disposal experts were called to the eastern edge of Tentsmuir Forest on Tuesday after the tail of an unexploded mortar emerged from the sands.
The coastguard was alerted to the incident after a passing cyclist noticed the object, about one foot in length and five inches in width, at around 1.30pm.
Dundee man Will Maraner (46) was also at the scene walking his dog, Ike, when he came across the startling discovery.
Not panicked by the potentially lethal object just inches from his feet, Mr Maraner pulled out his camera to take souvenir pictures.
He said, “I was out on the beach with the dog when I came across this object. Another guy was already there and called the coastguard.
“I had a good poke and pull at it but couldn’t free it. The dog was also trying to pull it out with his mouth.”
He added, “The coastguard arrived shortly afterwards and had a look.
“No-one knew how old it was but it looked to be in quite good condition.
“When I was pulling at it you could tell it was solid and very strong.”
After the alarm was raised the coastguard contacted the Ministry of Defence, who scrambled a team from Faslane Naval Base.
The area was cordoned off as the specialists carried out a controlled explosion at around 5.20pm.
Only last month a second world war railway wagon was also discovered in the Tentsmuir National Nature Reserve after the erosion of dunes.