Dan Mackay, 37, discovered the military tags under the earth beside the site of a World War Two anti-aircraft battery just outside London.
They represent almost every army regiment - including men who stormed the beaches of Normandy.
He stumbled on the site as he looked for military relics and was stunned to find thousands and thousands of dog tags from World War Two.
Military buff Dan believes they were some of the first metal tags made and due to be sent out to replace existing fibre ones that were used for most of the war.
He thinks the site he found was near a former factory which made them - and they somehow ended up buried.
Dan, of Stansted Mountfitchet, Essex, has already managed to reunite some of the tags with the soldier’s family.
In the last six months he has returned eight dog tags to their families - three of which have been returned to living veterans.
But he is keen to get as many of the 14,000 tags back to the families of the fighters - many of whom may have died in battle.
He said: “From hundreds of hours of research I’ve found out I have dog tags belonging to thousands of soldiers.
“That includes military medal winners, PoWs, foreign medal winners and hundreds mentioned in dispatches - and I still have thousands more to get through.”
Dan dug up the dog tags at a site near London while out on a hunt with fellow relic hunters Alan Tissington and Jay Hewitt.
They discovered thousands of dog tags over two days of digging at the area - the exact location of which they are not publishing for fear scavengers will flock there.
Dan said: “Everywhere we dug in this area we found dog tags.
“The finding of the tags didn’t seem to be slowing down at all, and in most places they were as lovely as the day they were thrown in,
“The excitement was almost unbearable, it was as if someone had lifted the lid on a treasure chest full of silver coins.
“I was sure that I stood there open mouthed for several minutes, before almost diving in head first.”
The military enthusiast, who has self-published two books on military history, also added he has “barely touched the surface” of the information about the dog tags.
“We returned to the site recently and in just four hours we recovered another 2000 dog tags - it’s crazy,” he said.
Mr Mackay believes the tags found at the anti-aircraft battery site had been manufactured for the soldiers named on them, but had never been issued.
He said: “Nobody has ever seen or heard of anyone ever having a metal dog tag during World War Two,
“They were always considered to be post-war - until we found these and the serial numbers proved them to be wartime dog tags.
“The most plausible conclusions are that they were made to replace all the original fibre tags - or that they were made to be issued at a point that didn’t happen.”
He added, “The only other thing we discovered at the site was evidence of lots and lots of burnt paper, which may have been the paperwork recording the details of all the soldiers.”
Dan at first struggled to find any details about who the men and women were - until late in 2016 that he discovered the website Forces War Records.
It stores records dating back to the pre-Napoleonic wars of the 18th century.
“It’s all gone a bit mad since I joined Forces War Records, I’ve had so many results and it’s really snowballed,” he said.
He said the best result came in February, with his first experience of returning a dog tag to the veteran himself after arranging it with the vet’s son on Forces War Records.
“Fred Bills had no idea that I had his dog tag with me, but happily spent over three hours sharing stories from his time as a driver during the war,” recalls Mr Mackay.
“He was surprised and happy to see his dog tag, let alone be told he could keep it - he tried to hand it back to me at first.”
Mr Mackay also praises fellow relic hunter Katey Mishler, who he says has been helping him from the United States.
He said: “It’s starting to feel like a full-time job - and certainly not one that normal people do.
“But we’re desperate to return the dog-tags we’ve found and I will travel nationwide, if that’s what it takes.”
Mr Mackay encourages people with any information or suspected link to the dog tags to contact him through the Extreme Relic Hunters Facebook page or by visiting www.extremerelichunters.com/fadt.
The British Army introduced identity discs in place of identity cards in 1907, in the form of aluminium discs.
During World War One and Two, service personnel were issued pressed fiber identity disks.
From 1960 these were replaced with stainless steel ID tags on a green nylon cord, two circular and one oval. The oval was withdrawn around 1990.