David Barrett is a professor of political science at Villanova University, where he teaches a course on U.S. intelligence, and is the co-author of “Blind Over Cuba: The Photo Gap and the Missile Crisis.”

The young man was employed by the National Security Agency for only a couple of years before feeling shocked at its intrusions into other countries’ affairs and even private mail addressed to U.S. citizens. He was also disgusted at the contrast between the idealistic language of the president, serving his second term, and the behavior of the government he headed.

The young man talked repeatedly with a close friend who also worked at the NSA. The two tried informing a member of Congress of the agency’s activities. But the representative — Wayne Hays (D-Ohio) — did not expose what they told him. So the two devised a plan to publicize what they considered the extraordinarily hypocritical actions of the government. They would travel secretly to a country where no extradition agreements could affect them and tell the press what the NSA had done.

It was the summer of 1960, and 29-year-old William Martin and 31-year-old Bernon Mitchell told their bosses they were going on a three-week vacation. On June 25, they took a cab from their homes near NSA headquarters in Maryland to National Airport, discussing chess during the ride. They flew to New Orleans and then Mexico City before making their way to Cuba and then — by way of a long boat ride — to the Soviet Union.

A month later, NSA officials obtained a warrant to open a safe-deposit box rented by Mitchell and learned of the defection. In August, the government announced that two mathematicians working for the NSA had defected but played down the significance. But on Sept. 6, 1960, the two walked into the elaborately gilded Soviet Journalists Union headquarters in Moscow and faced an audience of reporters from around the world, including the United States.

Under strong lights, the two cryptologists revealed far more than had ever been disclosed about U.S. intelligence-gathering activities since the NSA was created by secret executive order in 1952. The agency, they reported, “gathers communications intelligence from almost all nations of the world.” They emphasized their disenchantment over the NSA “intercepting and deciphering of the secret communications of its own allies,” naming France, Italy, Uruguay and others. The U.S. government had gone “so far as to recruit agents from among the personnel of its allies” by giving money to a “code clerk working in the Washington embassy of a United States ally for supplying information, which assisted in the description of the ally’s coded messages.” That ally was Turkey, they said.

They also revealed that the CIA’s spy flights over the Soviet Union — which had been exposed in the infamous downing of a U-2 a few months earlier — were not rare: For years the U.S. government had frequently sent military aircraft over the U.S.S.R. to gather intelligence.

A decade and a half before the Senate’s Church Committee would reveal that the U.S. government had attempted the overthrow of various foreign governments, Martin and Mitchell said just that: “Since going to work for the National Security Agency in the summer of 1957, we have learned that the United States government . . . secretly manipulates money and military supplies in an effort to bring about the overthrow of governments which are felt to be unfriendly to the United States.”

Citing press reports, they also claimed that the federal government had opened millions of pieces of mail sent from abroad to U.S. residents.

In sum, the United States had employed intelligence methods “as unscrupulous as it has accused the Soviet government of being.”

Whereas Edward Snowden’s recent revelations have provoked significant debate about whether the NSA’s activities are legal, properly monitored by Congress and justifiable, such a debate did not occur in 1960. Legislators and the press seemed interested in the revelations, but no one expressed sympathy for Martin and Mitchell. They were “self-confessed” traitors, said President Dwight D. Eisenhower. They “ought to be shot,” Harry Truman said. On Capitol Hill, the focus was on who erred in hiring Martin and Mitchell, who had brought about “one of the worst security breaches in American history.” After the government revealed that at least one of the two was gay, there was also debate about whether homosexuals were a threat to national security. (The press routinely referred to them as “close bachelor friends.” Rep. Francis Walter (D-Pa.), who would investigate the personnel security practices of the NSA, referred to Martin and Mitchell as “deviates” and “poor, unfortunate homosexuals.”)

But except for having to change its security clearance procedures, the NSA was largely unscathed by the controversy. Martin and Mitchell, who thought they had moved to a workers’ paradise, soon became disillusioned. They went on to lead long, unhappy lives in the Soviet Union. In contrast, such a quiet resolution seems unlikely for either the NSA or Snowden.