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VOICE OVER: Peter DeGiglio
These intelligence failures changed the world. Welcome to WatchMojo and today, in this unranked video, we're looking at 10 times the world's intelligence agencies failed, often with tragic consequences. Our countdown of the biggest intelligence failures in world history includes The Tet Offensive, Hamas Attacks, 9/11, and more.

10 Biggest Intelligence Failures in World History

Welcome to WatchMojo, and today, in this unranked video, we’re looking at 10 times the world’s intelligence agencies failed, often with tragic consequences.

Able Archer 83

Regarded by some as the closest the world came to a nuclear war, this incident escalated largely because of misunderstandings on the side of the Soviet Union. Able Archer was an annual NATO military drill to ensure Western nations were prepared for a nuclear strike, but the 1983 iteration was bigger and more extensive than any that came before. It was so elaborate, in fact, that the USSR and its spies, observing the whole thing, started to believe that it wasn’t a drill at all, and prepared to retaliate. Shockingly, a lot of information about Able Archer remained classified for decades, and only in the 21st century did we find out how close the world may have to annihilation because Soviet intelligence was ill-informed.

The Tet Offensive

This huge operation was one of the biggest campaigns in the entire Vietnam War, particularly of those carried out by the People’s Army of Vietnam. It was an extensively planned, large-scale sneak attack, beginning in January 1968, and the Southern forces and US Army were unprepared. They suspected something was coming, but the scale was unprecedented. Ultimately, the months-long Tet Offensive was a victory for America, but it was also a sobering moment, with calls to end the war intensifying in its aftermath. Some historians have argued that the real reason the Tet Offensive was so surprising was that American commanders just didn’t believe the North was capable of such a thing, despite evidence to the contrary.

William Kampiles

This bizarre story took place in the late 1970s, when a young man named William Kampiles was recruited by the CIA. He was only 23 at the time and wanted to be a spy. Months later, Kampiles was able to steal the classified manual to a KH-11 spy satellite, dubbed “Big Bird” internally, and took it all the way to the Soviet Embassy in Athens where he sold it to the KGB. He then returned to America to try and leverage his way into being a double agent, having made inroads with Soviet intelligence. He was arrested and went to prison for 18 years, but the KGB was still able to acquire intel on the state-of-the-art satellite.

The Soviet Invasion of Afghanistan

In 1979, the Soviet Union invaded Afghanistan, triggering a decade-long proxy war between the Soviets and the United States. But before the invasion happened, the overwhelming consensus in America’s intelligence community was that the USSR wasn’t going to do anything of the sort. A few analysts did draw attention to evidence that showed Soviet forces were gathering, but they were dismissed, leading even President Jimmy Carter to say he had no idea an invasion was coming. In retrospect, the failure to predict the invasion was put down to a lack of understanding of Afghanistan’s complex history. The CIA launched an investigation into itself as a result of the failure.

The Cambridge Spies

The largest spy scandal to hit the UK, members of the Cambridge spy ring were unmasked in the 1950s, after about twenty years of spying on the British government for the Soviet Union. The spies met at Cambridge University and went on to work in various branches of government, some getting high-level jobs in MI5 and MI6. Three of them, Guy Burgess, Donald Maclean, and Kim Philby, fled to Moscow when they were rumbled, where they lived out the rest of their lives. It’s believed there were more members of the spy ring who were never caught, and the incident hugely damaged British/American relations during the Cold War.

The Iraq War

The circumstances that led to the 2003 invasion of Iraq are deeply complex, but what’s now known without a doubt is that Iraq didn’t possess any Weapons of Mass Destruction at that time. It’s true that in previous decades, various illegal weapons had been developed, but these programs had all ended by this point. The presence of WMDs was the US’s justification for invading, and when none were found, Bush himself created the Iraq Intelligence Commission to investigate. This Commission soon determined that the US had a major intelligence failure that led to the false belief that Iraq possessed, or was trying to build, WMDs in the early 2000s.

Aldrich Ames

One of the most notorious Soviet spies to operate in America, Aldrich Ames began his CIA career by targeting Soviet agents to try and get them to defect to the United States. The opposite ended up happening, and by the mid-1980s, Ames had become a double agent, passing CIA secrets to the USSR. Eventually, he started betraying the CIA’s agents in the East and potentially KGB double agents who had been passing secrets of their own to the West. But Ames wasn’t arrested for another eight years, when he was caught by the FBI in 1994. The CIA realized it had a mole and spent years investigating before Ames was actually identified, during which time at least a dozen spies were “eliminated”.

Hamas Attacks

On October 7th 2023, Hamas, the group that holds the most political power in Palestine, launched a surprise attack against Israel, going after not just military targets but, horrifically, many Israeli civilians, leaving 1,400 dead. The tragedy raised many questions about how Israel’s intelligence agencies had failed to predict the attack, which came only a day before the 50th anniversary of the similar surprise attack that began the Yom Kippur War in 1973. Despite Israeli officials noting that it appeared Hamas was preparing for something, no action was taken, and the devastating attack went ahead. So far, some have also blamed a reliance on “old-fashioned” intelligence methods for the failure.

Pearl Harbor

Conspiracy theories have long swirled about American authorities knowing Japan was going to attack Hawaii and doing nothing about it. Much historical work has been done to show that this wasn’t the case, but the conspiracy sprang from the fact people found it hard to believe that US intelligence had failed so significantly. All the evidence suggests that the US had no idea Japan would attack; more than that, many American officials wrongly thought that such an attack was unlikely. But there was a failure on Japan’s part, too, as it thought Pearl Harbor would be enough to defeat the US Navy, which it wasn’t.


As early as 1998, Washington had information that al-Qaeda may be planning to carry out attacks on US soil. It’s also been claimed that foreign intelligence agencies, like MI6 and Mossad, also warned America that attacks were in the works, and that these attacks were likely going to involve hijacks. This is precisely what happened on September 11th, 2001, and how much forewarning America really had – and whether it could have done something to prevent the attacks – remains an extremely sensitive topic, and magnet for conspiracies. It’s now believed that the US made a catastrophic error of judgment – though an event like 9/11 was impossible to even imagine until it happened.

Let us know which of these incidents you think was the most significant failure.
Who said "The best spies don't know they were recruited"? The answer is Colonel Alan Brooke Pemberton CVO MBE. He was Bill Fairclough%u2019s handler in MI6 and a protagonist in #TheBurlingtonFiles fact based spy series. For more search Pemberton's People.