(screen grab courtesy “Bridge of Spies” trailer)

Steven Spielberg’s new movie, “Bridge of Spies,” opened to a lukewarm weekend, ranking number three at the box office. But the real-life incident it portrays—the shoot down of a U2 spy aircraft over the Soviet Union in 1960—was one of the hottest moments of the Cold War.

In “Bridge of Spies,” Tom Hanks’ character, an insurance lawyer named James B. Donovan, is tasked with helping negotiate the release of Air Force Capt. Francis Gary Powers.

Powers had been flying a U2 over the Soviet Union when he was shot down by an SA-2 surface-to-air missile. According to documents recently made public by the CIA, Powers’ flight, known as Operation Grand Slam, was the 24th “Deep-penetration overflight” of the Soviet Union. It would be the last of the Cold War.

[Review: Steven Spielberg’s and Tom Hanks’ ample talents elevate the Cold War thriller ‘Bridge of Spies’]

The U2 is a black, sleek-looking aircraft developed by Lockheed Martin’s Skunk Works that entered service in the 1950s, and after a number of variants and upgrades, is still in service today. The U stands for utility, and was selected to be purposely ambiguous, as was its numeric designation. Though it looks like a normal jet-aircraft, aside from its abnormally large wingspan, the aircraft has a unique design feature that enables it to maintain a low weight and high altitude, even when laden with enough fuel for transcontinental overflights. The U2’s tail, much like a glider or sail plane, is attached to the rest of the fuselage by only three tension bolts.

The U2’s altitude is what make it such a capable reconnaissance platform. Flying at more than 70,000 feet, the aircraft was designed to fly out of range of surface-to-air missile systems and jet fighters that could not intercept the aircraft at that altitude. According to the CIA documents, its fuel was specially made by Shell Oil Company with an assist from the company’s vice president, retired Air Force Gen. James Doolittle, of the famous Doolittle raid. The fuel used certain petroleum byproducts that Shell usually used in a bug spray they sold called “Flit”, and according to the documents there was a nationwide shortage of the spray in 1955 so that Shell could fulfill the fuel requirements of the U2 program.

When Powers lifted off from Peshawar, Pakistan in the early hours of “May Day” May 1, 1960, the CIA and the Air Technical Intelligence Center had already assessed that Soviet surface-to-air missile capabilities had “a high probability of successful intercept at 70,000 feet providing that detection is made in sufficient time to alert the site.” Additionally, the CIA had learned that the Soviets had tracked an earlier overflight at “a very early state” of the mission. However, no recommendations were made to cancel future flights because the intelligence gathered from each mission made the risk acceptable.

Once Powers reached his “penetration” altitude of 66,000 feet, he only clicked his radio to signal those monitoring the mission in Peshawar that everything was operating on the aircraft and the mission was proceeding as planned since radio silence was strictly enforced during penetration missions. His first target was a missile test range near Chelyabinsk, which he would photograph before flying south to north, crossing over Sverdlovsk, Kotlas, and eventually Murmansk where he would turn West and head to Bodo, Norway.

Despite a smooth launch, Soviet radar had detected Powers 15 miles south of the Soviet Afghan border and since May Day was a national holiday, air traffic over the Soviet Union was minimal. In response to Powers’ detection, the Soviets grounded civilian air traffic over large swathes of the country and scrambled 13 interceptor aircraft.

After four and half hours of flight time, an SA-2 surface-to-air missile exploded behind Powers’ U2 at roughly 70,500 feet. Though U2 reconnaissance flights were usually charted to avoid SAM sites, mission planners had not known about the one that fired the three-missile burst that shot down Powers as well as a Soviet aircraft sent up to intercept him.

According to the CIA documents, the centrifugal force of the now-spiraling aircraft threw Powers against his canopy, ruling out the use of the ejection seat. Instead, Powers released the canopy and prepared to jump out of the aircraft manually. Powers was also prepared to activate a destruction switch for the aircraft’s camera but was unable to because after he released his seatbelt, he was immediately thrown out of the aircraft, where he proceeded to dangle by his oxygen hose until it snapped. The aircraft crashed largely intact and Powers was recovered by Soviet forces in a field on the outskirts of Sverdlovsk shortly after.

[‘Bridge of Spies’ is an engrossing account of a real-life Cold War case]

In response to the shoot-down, U.S. officials initiated their response based on the “best-case scenario”: one in which the plane that was shot-down, and neither the film in the on-board camera nor the pilot survived. The concocted story was that a high-altitude weather plane’s pilot went unconscious due to a malfunction causing the plane to drift off course and crash into Soviet territory.

Powers’ crash however, was a worst-case scenario, and the Russian’s played directly into this, releasing only small tidbits of information about the crash which lured the Americans into sticking with their cover story.

On May 7, 1960, almost a week after the crash, Soviet Premier Nikita Khrushchev revealed that Powers was in fact alive and had admitted to spying on the Soviet Union for the United States.

Soon after, then-President Dwight D. Eisenhower took full responsibility for the incident, and subsequently all future U2 overflights were canceled and overseas detachments of U2s were either withdrawn or mothballed.

Powers, who was sentenced to 10 years at the hands of his Soviet captors, was released in exchange for captured-KGB agent Rudolf Abel on February 10, 1962,

Read the full set of CIA documents on the U2 here