The echo from the episode, though, serves as a reminder that powerful countries regularly spy on one another, which generally becomes a problem when it goes public or leads to misunderstanding or tragedy.
In 1983, a Soviet warplane shot down Korean Air Lines Flight 007 after it veered into Russian airspace at night, killing 269 passengers and crew members, including an American congressman. Moscow said the plane had been mistaken for a spy plane. In 2001, a Chinese fighter plane got too close to an American EP-3E Aries II reconnaissance plane gathering intelligence over the South China Sea, forcing it to make an emergency landing at a Chinese base.
“The United States and its allies sent espionage balloons over the Soviet Union back to the late 1940s,” said Michael Beschloss, author of “Mayday: Eisenhower, Khrushchev, and the U-2 Affair,” published in 1986. “They did this to detect any danger of an imminent Soviet surprise attack and to assess the size of the Soviet military complex so that Truman and Eisenhower could gauge how much they needed to spend on defense.”
Eisenhower, he added, “believed that such intelligence-gathering served the peace by averting an unnecessary arms race that could lead to war.” Starting in 1956, Eisenhower authorized the C.I.A. to secretly send U-2 planes over Soviet territory, gambling that their altitude of 70,000 feet would keep them undetected. At the same time, Eisenhower understood that the flights could be seen as an act of war and insisted on personally approving each one.
In fact, the flights were being detected. Khrushchev knew about them and was furious at the intrusions into Soviet airspace, but he made no public protest because he did not want to reveal his military’s inability to stop them until a more sophisticated missile was developed.
As the Paris meeting approached in 1960, Eisenhower wanted to avoid any chance of disrupting the gathering and ordered U-2 flights halted well in advance. But after bad weather postponed a mission before the meeting, Richard Bissell, the father of the C.I.A. program, persuaded the president to authorize a final flight on May 1, barely two weeks before the meeting scheduled for May 16.
“Even in the less conspiracy-minded age of 1960, some Americans wondered whether warlike figures in our Pentagon had deliberately sent the flight to destroy the summit,” Mr. Beschloss said. “Such questions will now be asked of the Chinese military.”