A chill wind whipped off the Warnow as a retired railroad worker shuffled through the streets of the port city of Rostock one winter night in 1956. He wore the drab clothes typical of East German residents. But when a second man appeared from the shadows, the elderly German revealed that he was wearing a pair of distinctive gold cuff links embossed with the helmet of the Greek goddess Athena and a small sword.

The second man wore an identical pair. Wordlessly, he handed the German a package of documents and retreated back into the shadows. The German caught a train for East Berlin, where he handed the package and the cuff links to a CIA courier. The courier smuggled them to the agency's base in West Berlin—to George Kisevalter, who was on his way to becoming a legendary CIA case officer.

The man who retreated back into the shadows was Lt. Col. Pyotr Semyonovich Popov, an officer of the GRU, the Soviet military intelligence agency. Three years earlier, Popov had dropped a note into an American diplomat's car in Vienna saying, "I am a Soviet officer. I wish to meet with an American officer with the object of offering certain services." He was the CIA's first Soviet mole, and Kisevalter was his handler. Popov became one of the CIA's most important sources through the 1950s, turning over a trove of Soviet military secrets that included biographical details on 258 of his fellow GRU officers.

It was Kisevalter who had decided on the cuff links as a recognition signal. He gave them to Popov before Moscow recalled the GRU officer in 1955, along with instructions: If Popov ever made it out of the USSR again and renewed contact with the CIA, whoever the agency sent to meet him would wear a matching set to establish his bona fides.

Popov renewed contact after he was assigned to Schwerin, East Germany, and the cuff links worked as intended. He fed Kisevalter information through the retired railroad worker for another two years. But after Popov was recalled to Moscow in 1958, he was arrested by the KGB. There are various theories on why he fell under suspicion. However, in a series of interviews two decades ago, Kisevalter told me it was the result of a botched signal: He said George Payne Winters Jr., a State Department officer working for the CIA in Moscow, "got the instruction backward" and mistakenly mailed a letter addressed to Popov at his home. The KGB spotted him in the act and fished the letter out of the mailbox. Popov was doomed.

The Soviets expelled Winters from Moscow in 1960, the same year they executed Popov—by firing squad, Kisevalter believed. He told biographer Clarence Ashley he doubted a rumor that Popov had been thrown alive into a furnace as a lesson to other GRU officers, who were required to watch.

Today, the cuff links rest in one of the most compelling and least visited museums in the United States. The museum has an extraordinary collection of spy gadgets, weapons and espionage memorabilia from before World War II to the present—more than 28,000 items, of which 18,000 have been cataloged—and hundreds are on display. But the museum is run by the CIA and housed at its headquarters in Langley, Virginia, eight miles outside Washington, D.C. The agency's entire campus is off-limits to the public, and the museum is open only to CIA employees, their families and visitors on agency business. By special arrangement, Smithsonian magazine was allowed to tour the museum, take notes and photograph select exhibits. Our guide through the looking glass was Toni Hiley, the museum's director. "Every day, CIA officers help to shape the course of world events," Hiley said. "The CIA has a rich history, and our museum is where we touch that history."

The Hi-Standard .22-caliber pistol is described in the exhibit as "ideal for use in close spaces or for eliminating sentries." Developed by Stanley P. Lovell, the chief of gadgets and weapons for the Office of Strategic Services, the CIA's World War II predecessor, the long-barreled weapon was flashless and silencer-equipped—designed to kill without making a sound.

The Hi-Standard .22 was said to be so quiet that President Franklin D. Roosevelt didn't hear it when it was fired in the Oval Office. (Dan Winters)

How quiet was it? According to Lovell's account, Maj. Gen. William J. "Wild Bill" Donovan, the chief of the OSS, was so eager to show off his agency's latest lethal gadget that he took a Hi-Standard and a sandbag to the Oval Office. While President Franklin D. Roosevelt was busy dictating to his secretary, Lovell wrote in his book Of Spies and Stratagems, Donovan fired ten rounds into the sandbag. FDR gave no notice and never stopped talking, so Donovan wrapped his handkerchief around the still-hot barrel and presented the weapon to the president, telling him what he had just done.

Roosevelt is said to have responded, "Bill, you're the only wild-eyed Republican I'd ever let in here with a weapon." Donovan gave FDR one of the guns, Hiley told me: "It was displayed in Hyde Park. But the OSS came one day and said they'd have to take it back because it was classified."

As the Nazi regime collapsed in 1945, a young OSS officer sat down to write a letter to his son in the United States. "Dear Dennis," he wrote,

The man who might have written on this card once controlled Europe—three short years ago when you were born. Today he is dead, his memory despised, his country in ruins. He had a thirst for power, a low opinion of man as an individual, and a fear of intellectual honesty. He was a force for evil in the world. His passing, his defeat—a boon to mankind. But thousands died that it might be so. The price for ridding society of bad is always high. Love, Daddy

The card on which Richard Helms was writing was a piece of Adolf Hitler's personal stationery. It bore a gold-embossed eagle holding a swastika above the Nazi leader's name. To the right was printed the word "Obersalzberg," referring to Hitler's retreat high in the Bavarian Alps above Berchtesgaden.

As World War II ended in Europe, future CIA director Richard Helms found distinctive stationery to write a letter home to his young son. (Dan Winters)

"I found the letter when I was in high school, in a bunch of scrapbooks my mother kept, but I had no idea of its significance," Dennis Helms, now 72 and a lawyer in New Jersey, told me. "It just sat there in a suitcase I kept under my bed, tucked away in a scrapbook with the Christmas pictures." He donated it to the agency in 2011.

He says the letter gave him insight into the secretive and private nature of his father, who served as CIA director from 1966 to 1973, when he was dismissed by President Richard M. Nixon. Richard Helms died in 2002. "The letter was a very emotional expression for my father," he said. "He was not known for emotions. He was all about the facts. He was the most understated guy on the planet.

"I knew early on he was in the CIA. When friends asked, I would say he worked for the State Department. They would ask what he did and I said, 'I don't know.' They said, 'You must be pretty stupid.' "

When Dennis asked his father how he had managed to snare a piece of Hitler's stationery, he received a vague answer. Although the letter was dated V-E Day—May 8, 1945—Richard Helms wasn't even in Germany that day, although he was later stationed in Berlin. Dennis says he wasn't surprised that his father's life remained surrounded by mysteries: "I found things in the museum that he had never mentioned."

In spy fiction, an electronic bug is usually small enough to fit inside a cellphone or to be sewn into the lining of a jacket an unwitting victim takes to the cleaners. In spy life, an electronic bug can be ten feet long.

A metal reinforcing bar was also an electronic bug—one of dozens the KGB planted in the U.S. embassy in Moscow. (Dan Winters)

The bug in this instance is an insulated metal reinforcing bar, one of dozens the KGB embedded in the walls of the U.S. embassy in Moscow, and thus a relic of one of the most awkward episodes in the U.S.-Soviet détente. In a purportedly helpful move, the Soviet Union offered to sell the United States precast concrete modules for the building, supposedly to ensure that it would be up to code, and the United States accepted. But mid-construction inspections beginning in 1982, including X-rays, revealed that the Soviets were turning the building into a huge antenna, with some bugs so sophisticated they could transmit each keystroke from the embassy's IBM Selectric typewriters. After that, the top floors of the embassy were torn down and replaced by a secure "top hat" of four floors. The project took more than four years—and was done by American contractors.

Just two weeks after the terrorist attacks of September 11, 2001, the CIA began inserting personnel into Afghanistan to prepare for the U.S. response to Osama bin Laden and his compatriots in Al Qaeda, and the agency is still active there. The museum's Afghan Gallery has objects ranging from the patriotic—such as the "Don't Mess With the U.S." T-shirt an agency logistics officer bought after she found out she would be deployed in 2003—to the bemusing, such as the photograph of a CIA K-9 explosives-detection team in which the security measures extend to obscuring not only the faces of the three men in the frame, but the dog's face as well. Among the most sobering are those related to the hunt for bin Laden.

After the raid that killed Osama bin Laden, a brick was retrieved from his compound. (Dan Winters)

The search took ten years, from bin Laden's disappearance into the Afghan mountains soon after 9/11 to the CIA's picking up the trail of a courier that led to a compound in Abbottabad, in northeastern Pakistan, in 2011. Surveillance photographs showed a tall man occasionally pacing in the compound's courtyard. Could it be bin Laden? The agency developed evidence that it was, but analysts could not be sure. After an extensive debate, the Obama administration made a decision: Any assault would be made by a team of Navy SEALs working under the aegis of the CIA.

Technicians at the National Geospatial-Intelligence Agency, mapmakers for the intelligence community, built three scale models of the compound, Hiley said. The original was used to brief the assault team and President Obama; of the two created for the historical record, one is in the CIA museum. The SEALs also trained on a full-scale mock-up at an undisclosed CIA site. "We don't say where the training on the mock-up took place, but it was one of the CIA's covert sites," Hiley said. The training was widely reported to have taken place in North Carolina. The assault team destroyed parts of the mock-up every day, Hiley said, but it was rebuilt.

A Russian-made assault rifle that was found next to his body is presumed to have belonged to him. (Dan Winters)

At the CIA, then-director Leon Panetta awaited word from the White House. If anything went wrong, President Obama would take the blame, but so would he. At 10:35 a.m. on April 29, 2011, Panetta got a call from the president's national security adviser. He reached for a sheet of stationery bearing the words, "The Director, Central Intelligence Agency, Washington, D.C. 20505" and began writing a memo for the record, which is preserved under glass at the museum:

"Received phone call from Tom Donilon who stated that the President made a decision with regard to AC1 [Abbottabad Compound 1]. The decision is to proceed with the assault….The direction is to go in and get Bin Ladin and if he is not there, to get out. Those instructions were conveyed to Admiral McCraven at approximately 10:45 AM." In the moment he added an extra "c" to the name of then-Vice Adm. William H. McRaven, commander of the U.S. Special Operations Command.

The raid proceeded shortly after 1 a.m. on May 2 in Pakistan. After it succeeded, some of the SEALs told agency debriefers the mock-up had been so accurate they felt as if they'd been to the compound before. The museum has two artifacts from Abbottabad: a brick from bin Laden's compound and an assault rifle, a Russian-made AKMS modeled on the Kalashnikov AK-47 but, for reasons unknown, with counterfeit Chinese markings. "The rifle was found next to bin Laden when he was killed," Hiley said. "So we assume it was his rifle."

Single Shot

The Liberator, or FP-45, never had the cachet of the silent Hi-Standard .22—it fired just one .45-caliber bullet, and that bullet had a tendency to wobble off course beyond a range of 25 feet. But the weapon was designed to be air-dropped to resistance forces behind enemy lines, as much for its psychological value as its dubious firepower. "The idea was, you would use the gun to liberate a better weapon from an enemy," Hiley explained. In the summer of 1942, "GM made a million of these in three months, and thousands were shipped to China." The staff of Gen. Dwight D. Eisenhower had little enthusiasm for the weapon, and authorized the dropping of only 25,000, for the French resistance.