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Two lines of trenches face off across No Man's Land. A soldier marches, rifle in hand, along a ditch. These are instantly familiar images of World War I — but this is Britain, a century on and an English Channel away from the battlefields of the Western Front.

This overgrown and oddly corrugated patch of heathland on England's south coast was once a practice battlefield, complete with trenches, weapons and barbed wire. Thousands of troops trained here to take on the German army. After the 1918 victory — which cost 1 million Britons their lives — the site was forgotten, until it was recently rediscovered by a local official with an interest in military history.

Now the trenches are being used to reveal how the Great War transformed Britain — physically as well as socially. As living memories of the conflict fade, historians hope these physical traces can help preserve the story of the war for future generations.

"We've now lost our First World War veterans. You're not going to get a firsthand account," said Richard Osgood, an archaeologist with the Ministry of Defense, which owns the land. "In many ways, the truest witness is the archaeology and the legacy left behind."

The trenches, near the town of Gosport, about 80 miles (130 kilometers) south of London, were rediscovered a few months ago by Robert Harper, head of conservation at the local council. A military history buff, he noticed some crenellated lines on a 1950s aerial photograph of the area, and was startled to recognize the pattern of "the classic British trench system."

He was even more surprised when he had a look at the land — a local picnic spot — and found the contours of the trenches still clearly visible under a thick covering of bracken, gorse and grass. He could make out a front-line trench and several reserve rows, along with communications trenches and forward observation posts. And then there was an opposing set, 300 yards (meters) away.

"It was one of those jaw-dropping moments," Harper said.

"I've got five relatives buried on the Western Front. I think to myself, 'Did any of them train here?'"

Several other sets of practice trenches have been found in Britain, but this is easily the most extensive. Conservation body English Heritage, which announced the find Friday, said the task of mapping and documenting the site has just begun. There were no immediate plans to turn it into a tourist site or build a museum around it.

The discovery is already providing ammunition for those who reject the "lions led by donkeys" view of the war, which argues that incompetent officers led ill-prepared troops into needless slaughter.

Historian Dan Snow said the elaborate mock battlefield "shows how seriously they took the business of training."

"They had to send the guys out to France to do the hardest of tasks, something no one had done before, and that is defeat the German army when they were dug in," Snow said. "How to break that deadlock? Well, the answer is right here in front of us. Massive, massive preparation."

The find is being used to launch a campaign, Home Front Legacy, which aims to record as many physical traces of the war as possible. Even though the four-year conflict was largely fought outside Britain, the war transformed the country's landscape in ways that have often been forgotten.

It's hoped amateur historians will comb family archives, local newspapers and other sources for evidence of everything from military bases and prisoner-of-war camps to munitions factories, pillboxes and listening posts.

"We're going to crowd-source this project," Snow said. "We're going to build a picture across the U.K. of the physical remnants of the First World War."

The project has the support of the defense ministry, which turns out to be keen on archaeology — perhaps unsurprisingly, since it owns 1 percent of Britain — and enlists volunteer soldiers to help with exploration on its lands.

Osgood said the aim at the mock battlefield is "to repopulate the landscape," to tell the stories of some of the troops who trained there. Soldiers from Britain, Canada, New Zealand and the U.S. all passed through this area, close to the major naval base of Portsmouth, on their way to the front.

It would only take the tiniest of objects, such as a lost cap badge, to provide a clue.

"These were real men in a real-life situation going out and sacrificing their lives," Harper said. "That emotional, human story — I'd love that to be the meat put on the bones of what we have."

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Online: www.homefrontlegacy.org.uk

Jill Lawless can be reached at http://Twitter.com/JillLawless