One day, a Nazi memorial was found by park service

Discovery on federal land in 2006 had a classic D.C. back story, including FBI director J. Edgar Hoover

washington» A team of power company workers were trudging through a seldom-visited thicket in Southwest Washington when they spotted something odd in a ditch.

Protruding from the grass was a rectangular slab of granite.

They looked closer, and an inscription on the surface came into focus. What they saw astonished them.

It was a memorial. In honor of Nazi spies. On U.S. government property.

“In memory of agents of the German Abwehr,” the engraving began, “executed August 8, 1942.”

Below that were six names and below those was another cryptic line: “Donated by the N.S.W.P.P.”

News of the unsettling discovery soon reached Jim Rosenstock, who worked in resource management for the National Park Service and also happened to be a local history buff. He was curious, but also skeptical. How could someone have planted such an item there? And why? And — above all — who?

“I kind of started doing a little bit of my own research,” Rosenstock recalled of that day in 2006 when he began to help unravel an only-in-Washington mystery, complete with World War II espionage, nationwide panic, a mass electrocution, J. Edgar Hoover chicanery and white supremacists.

At the start of World War II, Rosenstock discovered when he began his research, Adolf Hitler had been determined to show the world just how susceptible America was to a Nazi attack, so he ordered his military to devise a plan.

The high command, according to a 2002 Post story, recruited eight Germans for the mission. In teams of four, the men were loaded onto a pair of U-boats, one destined for Jacksonville and the other for a beach near the tip of Long Island.

On June 13, 1942, the New York group reached shore — and was almost immediately discovered by an unarmed Coast Guardsman on foot patrol. The men escaped, but by morning, the Coast Guard had unearthed the Germans’ buried supplies: fuses, pre-made bombs and four crates of TNT.

That wouldn’t have mattered to their leader, George John Dasch, who hadn’t intended to wreak devastation on Hitler’s behalf anyway. When the group reached New York City, he and a comrade decided to turn the others in, so Dasch phoned the FBI.

Four days later, he took the $82,000 he’d been given for the operation — more than $1 million in today’s money — and boarded a train for Washington. There, he met with FBI agents, whom he expected to welcome him as a hero. They didn’t.

J. Edgar Hoover, the infamous head of the bureau, recognized an opportunity. In late June, with all eight men caught, Hoover announced their capture and claimed credit for his agency. He made no mention of Dasch. In midsummer 1942, seven U.S. Army generals found all eight men guilty but left their punishment to the president. He sentenced six to death and two, including Dasch, to lengthy prison terms, though both were deported after the war.

Rosenstock quickly learned the back story of the six Nazi spies listed on the stone, but another question remained: Who had placed it there?

The line at the bottom — referencing the “N.S.W.P.P.” — offered a clue.

Until the mid-1960s, the National Socialist White People’s Party had gone by a more familiar name: the American Nazi Party. According to the Southern Poverty Law Center, the group’s founder, George Lincoln Rockwell, had given it the new title shortly before his assassination in 1967.

By the 1970s, though, the group had begun to split apart and had lost much of its relevance, leading Rosenstock to believe the Nazi memorial dates back to that time.

Then, the Park Service had to decided what should be done.

“It was an illegal monument,” Rosenstock said. “And we certainly did not want to be hosting a site for midnight rituals on Hitler’s birthday.”

In 2010, under the direction of a museum curator, a fork lift exhumed the granite block and lowered it into a truck. The stone, tagged OXCO-475, now spends its days beneath a protective blanket on a shelf at a storage facility in suburban Maryland. Park Service staff asked that The Post be no more specific than that.