A World War I dog tag found in a French paddock has been returned to the digger's family after an Australia-wide search.

French student Valentin Henon found the battered metal disc in a field near his home in northern France in 2012 while using his metal detector.

Enlisting the help of Philippe Clerbout from a French metal detection history group, they identified the dog tag as belonging to Australian shearer Cyril McCarthy who enlisted in Narrabri in 1916. He saw action at Messines and Passchendaele as a private in ‘C’ Company, 33rd Infantry Battalion of the Australian Imperial Force.

Pte McCarthy’s grandson Bernie McCarthy, from Collaroy, Sydney, was found by Lieutenant Colonel Glyn Llanwarne OAM of Lost Medals Australia after a story was published by ABC News Online in August 2013.

Today the dog tag was returned to Pte McCarthy’s family at the Anzac Memorial in Sydney.

The French history enthusiasts sent the dog tag by courier as they were unable to travel to Australia. Their parcel to Mr McCarthy included two letters and a Rising Sun ‘collar dog’, a pin worn on Australian soldiers’ uniform lapels during WWI.

Cyril McCarthy and his bride Frances on their wedding day in 1919. ( Supplied: McCarthy family )

Mr McCarthy is thrilled to have received the dog tag, letters and ‘collar dog’.

“I’m extremely happy and proud. It’s an incredible feeling and so gratifying to have it again after it sat there in the ground for so many years,” he said.

“For Philippe and Glyn to have gone to so much trouble to find me and return the dog tag has made me extremely pleased.”

Initially it was unclear how the dog tag came to be found in Campagne-les-Boulonnaise as the area was not fought over during WWI.

Australian War Memorial historian Aaron Pegram reviewed Pte McCarthy's service records and established his movements throughout the war.

After he was wounded in the left arm near Messines in Belgium on June 5, 1917, he was moved further to the rear to the 1st Casualty Clearing Station at Bailleul. From there, he was transferred to a Canadian hospital on the coast at Boulogne and then to a rehabilitation facility in France.

“The ambulance wagon on which Pte McCarthy was travelling would have driven through Campagne-les-Boulonnaise on its way to the hospital at Boulogne,” said Mr Pegram.

“Given that McCarthy was wounded in the arm, it is plausible his identity discs were removed so his arm could be properly treated.

Pte McCarthy returned to the trenches after injury

“Accepting this to be the case, I’m pretty confident we can say McCarthy parted ways with his identity disc at Campagne-les-Boulonnaise somewhere between 7 and 11 June, 1917,” said Mr Pegram.

Pte McCarthy’s service record sheds light on his personality and on life for the troops in the appalling conditions of the Western Front.

It reveals he was sick on several occasions and that he was reported for drunkenness on duty and for being in town without a pass. These resulted in the payment of a 10 shilling fine or disciplinary action recorded as “Field Punishment No. 2” for a period of 14 or 28 days.

The Australian War Memorial explains this punishment was awarded by court martial or by the commanding officer for offences committed on active service.

Cyril McCarthy's dog tag together with a WWI 'collar dog' which was worn on the collar of a soldier's uniform. ( Glyn Llanwarne )

Field Punishment No. 1 involved heavy labouring, possibly while restrained in handcuffs and also tied to a post. In contrast Field Punishment No. 2 meant the offender was not tied to a fixed object.

Pte McCarthy’s service record also reveals he sustained two injuries. After recovering from his wound in 1917 he was sent back to the trenches but on May 10, 1918, he sustained a gunshot wound to the left hand. It was so severe that he was invalided to the United Kingdom and was eventually honourably discharged in June 1919.

He went on to marry, raised three sons and lived in Arncliffe, Sydney, where he worked as a sheet metal worker and died in 1979, aged 88.

Lt Col Llanwarne says the outcome of the search has been very rewarding.

“It’s pretty exciting because of where the dog tag has been for the past 96 years,” he said.

“It has survived another world war and despite the ravages of time, it’s in good condition for the family.”

Mr McCarthy now plans to put the dog tag in a presentation box where he says it will hold pride of place in his home.

“I feel the French people are very appreciative of the soldiers who fought on their soil,” he said.

“It’s a big thing for them to show their appreciation for the sacrifice of so many young men.”

The last of Pte McCarthy's three sons Leo died a month before Mr McCarthy was located and told of the find.