Sometime in 1943, not long after construction of the Pentagon had been completed and the great building first opened its doors for business, reports of a ghost began circulating among the military and civilian personnel working there. But it wasn’t just any ghost. It was a U.S. Army major who seemed to suddenly pop out of a wall in one of the large bays where the Army’s Ordnance Division had its offices. One minute there would be no one there and then a second later, there he was, hurrying past the rows of desks like he belonged there, but avoiding eye contact and then turning and disappearing into the stream of people walking along outside corridor. Weeks might go by without a sign of him, then he’d suddenly pop out of the wall again, sometimes with a bag in hand, and before anyone could ask him who he was and what he was doing there, he’d be gone.

It wasn’t difficult for people to accept that he might just actually be a ghost. After all, great buildings do have a way of attracting a ghost or two under its eaves, and even if the Pentagon was, at that point, not even a year old, it was already iconic. Besides, it was no secret that more than a few lives had been lost during its construction. Most were workmen, but no reason it could not have also included one or two of the hundreds of officers from the Army Corps of Engineers who oversaw every facet of the Pentagon’s construction. Perhaps the ghost officer might be one of them.

Then one day, the ghost was spotted again, but this time, instead of giving everyone the slip, they caught him. He wasn’t a ghost at all, but a major in the Corps of Engineers named Robert Furman, and he had a secret. Even though Furman officially had no business even being inside the building, he had something nobody else inside the Pentagon had. He had his very own secret “pad” hidden there inside the walls.

Furman explained that two years earlier he had been a deputy of Gen. Leslie R. Groves, the man who’d been in charge of the Pentagon’s construction. They all knew about Groves, the man who, with a massive army of workmen and construction equipment, took a large worthless tract of tidewater swampland and in a little over a year’s time, built the world’s largest office building on it. Groves was a legend.

But Groves had not been an easy man to work for. He was a notoriously exacting, hard driver who ran through subordinates at a fearful rate, firing those who didn’t perform and replacing them until he found ones that did. Furman was one of the few who actually seemed to thrive under Grove and soon became his Number Three. The Pentagon’s construction went on non-stop,, with three eight-hour shifts that each employed thousands of laborers. Furman was there at all hours, especially during night shifts, checking to make sure the people clocked in were actually working. The ones he caught loafing and getting drunk were fired on the spot. In fact, Furman might well have been responsible for firing Jack Kerouac, the future author of On the Road, who briefly worked there manning a wheelbarrow.

Even though Furman was billeted only a few miles away in Washington, D.C. he’d go days without leaving the work site. Rather than be unnecessarily away, he had a small, windowless apartment built inside the building, between the walls. There he and other officers could catch a few hours sleep, shower, and be back on the job, which it seemed was all the time.

But of course, as these things often do, once construction got completed, the men involved in building the Pentagon moved on to other projects. But when they did, knowledge of the hidden apartment somehow failed to get passed on to the building’s new management. When his new job sent Furman back to the Pentagon for some meetings, he was surprised to find the apartment undiscovered and exactly as he’d left it.  Since his work regularly brought him to Washington, rather than have to deal with the city’s notorious shortage of hotel rooms, Furman simply started sneaking back to the Ordnance Bay, waiting till no one was looking, then popping open the wall panel just enough to slip inside his pad, spending the night, and slipping out again in the morning.

Furman’s captors made him hand over the keys to his secret apartment. After that they let him go, giving him the stern warning not to show his face back there unless it was on official business. Doubtless, Furman’s ears burned a little getting caught and treated like that, but on another level it probably amused him no end. Maj. Robert Furman was a man of many secrets, and the one he’d just given up was by far of the least consequence.

What his captors never learned was that, while Furman might not have been a ghost, what he actually was, to use the parlance of later decades, was a “spook.” His wartime exploits were among the most incredible ones of World War II.

Groves had accepted the Pentagon assignment on the promise that once it was completed he’d be given a combat command. But the War Department was so impressed by his performance managing such a complex and demanding project that they immediately reneged on their promise and handed him an even more difficult and critical task. But it was so secret that they wouldn’t provide any details of what it involved until he accepted the assignment and was sworn into office. That was when Groves learned he was in charge of something called the Manhattan Project, which involved developing and building an atomic bomb. They had to build it using tens of thousands of workers, the vast majority of whom had absolutely no idea what the point of any of their activities would be, and they had to get it built before the Nazis finished the one that they also were most certainly building, though no one actually knew for sure.

Once Groves accepted the job, he immediately brought Furman aboard as his head of foreign intelligence, and ordered him to use any and every means to find out exactly how far along the Germans were in their nuclear bomb project. For that reason, Furman had spent months traveling back and forth all over the country visiting research laboratories and universities in order to meet with scientists and pick their brains about what their German counterparts might be working on. His travels routinely brought him to Washington, a wartime capital already notorious for its lack of hotel rooms, which was why Furman kept returning to his secret bachelor pad.

Not long after, Furman went overseas in order to get closer to the enemy. At one point he directed Swiss agents to take water samples from different spots on the upper Rhine and Lake Constance to check for evidence of the heavy water used in German nuclear research. On another occasion he sent the legendary Jewish-American spy, polymath and former major league ballplayer Moe Berg to a physics conference in Zurich, Switzerland in order to buttonhole German nuclear physicist Werner Heisenberg and find out how far the German nuclear effort was progressing. If it was two years ahead of the American program, as Furman feared, Berg was instructed to kill Heisenberg on the spot. Luckily for Heisenberg, Berg quickly determined that the Nazi bomb was lagging at least two years behind the Americans.

Following the Allied invasion of France in 1944, Furman and his agents traveled with the Allied armies, racing across France and into Germany in search of German nuclear scientists and German nuclear technology. In Belgium he came under sniper fire while looking for uranium. In Toulouse, he found 31 tons of it, which he had sent back to Los Alamos. When he found Heisenberg and a group of his colleagues, Furman had them all arrested and hidden away in a special prison facility, where he hoped the Russians could not find them and where they could consider, at their leisure, the advantages of lending their talents to the American effort.

Back in Los Alamos following the German surrender, Groves ordered Furman to escort some of the processed uranium to Tinian Island in the Pacific, where it’d be loaded aboard the atomic bombs being assembled there. Furman and his cargo traveled aboard the ill-fated cruiser USS Indianapolis, which, four days after unloading its secret cargo, was torpedoed and sunk with the loss of more than 800 men. Furman was one of the very few who watched the Enola Gay take off for Hiroshima, fully aware of what was going to happen.

After the war, Furman returned to civilian life. He settled in Bethesda, Md. and set up a construction company that built everything from single-family homes to churches and overseas American embassies. He married and raised a family, joined the local Rotary, stayed active in the Episcopal Church and sang baritone in a barbershop quartet. Though he was proud of his wartime experience, he never talked about it. It was only much later, toward the end of his life, that Furman realized that unless he told the story, several of the more fascinating and colorful chapters of World War II would pass forgotten into history. He started talking publicly about it. Shortly before his death in 2008, he even led a group of reporters and news camera crews back to the Pentagon where he gave them a guided tour, visiting his old offices and telling them stories about Gen. Leslie Groves and its amazing feat of construction. While he was surprised at how little the inside of the building had changed in the nearly sixty years since he’d last been there, of his secret wartime hideaway, he could find no trace at all.