This article was originally published on the Huffington Post.

What’s the number one military threat to the U.S.?

  1. Terrorism
  2. A deliberate nuclear attack
  3. Accidental nuclear war with Russia

Based on the recent political debates, you’d think it would be 1 or 2, but if you do the numbers, 3 wins hands down. Here’s why. Let’s compare the expected number of Americans killed during the year ahead, i.e., the number of Americans who’d get killed if the threat comes true times the probability of this happening during the coming year. For terrorism, one of the worst-case scenarios is a nuclear explosion in downtown New York killing millions of people. If we very pessimistically multiply this by a 10% chance of happening in 2016 (it’s probably much less likely), the expected number of casualties is a few hundred thousand per year.

For an all-out nuclear war with Russia, there’s a huge uncertainty in casualties. If nuclear winter is as severe as some modern forecasts and ruins global food production with freezing summers for years, then it’s plausible that over 5 billion of the 7.4 people on Earth will perish. If for some poorly understood reason there’s no nuclear winter at all, we can use a 1979 report by the U.S. Government from before nuclear winter was discovered, estimating that 28%-88% of Americans and 22%-50% of Soviets (150-450 million people with today’s populations) would die.

What’s the chance of this happening during the year ahead? Before answering, please check out this timeline of near-misses when it almost happened by mistake (highlights below). John F. Kennedy estimated the probability of the Cuban Missile Crisis escalating to nuclear war between 33% and 50%, and near-misses keep occurring regularly. Even if the risk of accidental nuclear war is as low at 1% per year, the expected deaths are 1.5-50 million people per year depending on your nuclear winter assumptions, way more than for terrorism. It’s likely that the chance of a deliberate unprovoked all-out nuclear attack by the U.S. or Russia is much smaller than 1%, given that this entails national suicide with over 7,000 nuclear weapons on the opposing side, many on hair-trigger alert.

A robust defense against terrorism and belligerent adversaries is clearly crucial, but U.S. military strategy can’t afford to be soft against the greatest threat of all: accidental nuclear war. When you hear about the U.S. plan to spend about $1 trillion modernizing and upgrading our nuclear arsenal, it at first sounds like a step in the right direction, reducing this risk. Unfortunately, looking at what the money is actually for reveals that it instead increases the risk. Please check out the disturbing incidents below: Which of these risks would be reduced by the planned more accurate missile targeting, improving first-strike incentive? By the new nuclear-tipped cruise missile? By the new gravity bomb? None! We’re spending money to make ourselves less safe by fueling a destabilizing arms race. We’ll be safer if those 1 trillion dollars were spent on non-nuclear parts of the U.S. military and on strengthening our society in other ways.

Top-10 list of near-misses

(Sources and more incidents here.)

10) January 1, 1961: H-bombs Dropped on North Carolina
A bomber was flying over North Carolina, when it lost a wing, and two of its nuclear bombs fell to the ground in Goldsboro, NC. One of the bombs broke on impact after its parachute failed. The other landed unharmed, but five of its six safety devices also failed. Defense Secretary Robert McNamara had this to say: “by the slightest margin of chance, literally the failure of two wires to cross, a nuclear explosion was averted.” (Center for Defense Information 1981; McNamara et al. 1963, p. 2). If this Hydrogen bomb would have detonated, could it have been misinterpreted as Soviet foul play?

9) October 24, 1962: Soviet Satellite Explodes During Cuban Missile Crisis
In the middle of the Cuban Missile Crisis, a Soviet satellite entered its orbit but exploded soon after. Not much is known about the event or U.S. reaction to it because the records are still classified. However, many years later, Sir Bernard Lovell of the Jodrell Bank Observatory noted that, “the explosion of a Russian spacecraft in orbit during the Cuban missile crisis… led the U.S. to believe that the USSR was launching a massive ICBM attack.”

8) January 25 1995: Norwegian Rocket Mistaken for ICBM
After the Cold War had ended, a Russian early warning radar detected a missile launch off the coast of Norway with flight characteristics similar to those of a U.S. submarine-launched ballistic missile. Fearing that it could be the first move in a larger attack, Russian nuclear forces quickly went on full alert. Russian President Boris Yeltsin activated his “nuclear football” and retrieved launch codes, preparing for a retaliatory launch. Fortunately Russian satellites monitoring U.S. missile fields did not show any additional launches, and Russian leaders declared the incident a false alarm. The event detected was actually the launch of a Norwegian scientific rocket on a mission to study the aurora borealis. Norway had notified countries, including Russia, in advance of the launch, but the information had failed to reach the correct Russian personnel.

7) October 26, 1962: US F102A Fighters vs. Soviet MIG interceptors
On the evening of October 26, during the Cuban Missile Crisis, a U.S. U2 spy plane accidentally entered Soviet air space. Soviet MIG interceptors took flight, with orders to bring it down. The U.S. pilot was ordered by commanders to fly back to Alaska as quickly as possilble, but he ran out of fuel while still over Siberia. He sent out an SOS, and F-102A fighters were sent up to escort him on his glide back to U.S. ground. The F-102A jets were loaded with nuclear missiles and the pilots had been given orders to shoot at their own discretion.

6) June 6, 1980: Faulty Chip Signals Soviet Attack
Early in the morning of June, 3, the warning displays at command centers began showing varying number of missiles had been launched toward the United States, and nuclear retaliation immediately commenced. However, personnel were able to determine in time that this was a false alarm as the varying missile numbers weren’t logical. Three days later, before the cause could be determined, the same thing happened again, and again B-52 crews and missiles were nearly sent out in retaliation. A faulty chip in the computers was finally found to be the cause of the display problems at the command posts.

5) November 11, 1983: Soviets Misinterpret U.S. Nuclear War Games
NATO conduced a massive command post exercise simulating a period of conflict escalation November 2-11 1983, culminating in a simulated DEFCON 1 coordinated nuclear attack against the Soviet Union. The exercise was highly realistic and debuted a new, unique format of coded communication, radio silences, and the participation of heads of government. Unbeknownst to NATO, this triggered extreme alarm on the Soviet side, where analysts feared that it was a cover for an actual nuclear attack, conveniently timed to coincide with their Revolution Holiday. Soviet nuclear missiles were placed on high alert, readied for launch. The climax came on the morning of November 11, when the Soviets intercepted a NATO message saying that U.S. nuclear missiles had been launched against them. Robert Gates, then deputy director of intelligence at the CIA, later said: “We may have been at the brink of nuclear war and not even known it.”
This incident is the subject of the British 1988 documentary The Brink of Apocalypse. It’s sobering to consider what might have happened if an independent incident such as the September 26, 1983 false alarm or the 1995 Norwegian Rocket Launch would have randomly occurred on November 11, 1983 instead.

4) November 9, 1979: Simulated Soviet Attack Mistaken for Real
Computers at NORAD headquarters indicated a large-scale Soviet attack on the United States. NORAD relayed the information to the Strategic Air Command (SAC) and other high-level command posts, and top leaders convened to assess the threat. Within minutes, U.S. intercontinental ballistic missile (ICBM) crews were put on highest alert, nuclear bombers prepared for takeoff, and the National Emergency Airborne Command Post–the plane designed to allow the U.S. president to maintain control in case of an attack–took off (but without President Jimmy Carter on board). After six minutes, satellite data had not confirmed the attack, leading officials to decide no immediate action was necessary. Investigations later discovered that the incident was caused by a technician who had mistakenly inserted a training tape containing a scenario for a large-scale nuclear attack into an operational computer. In a comment about this incident in a letter designated Top Secret (since declassified), senior U.S. State Department adviser Marshall Shulman said that “false alerts of this kind are not a rare occurrence. There is a complacency about handling them that disturbs me.”

3) September 9, 1983: Soviet Union Detects Incoming Missiles
A Soviet early warning satellite showed that the United States had launched five land-based missiles at the Soviet Union. The alert came at a time of high tension between the two countries, due in part to the U.S. military buildup in the early 1980s and President Ronald Reagan’s anti-Soviet rhetoric. In addition, earlier in the month the Soviet Union shot down a Korean Airlines passenger plane that strayed into its airspace, killing almost 300 people. Stanislav Petrov, the Soviet officer on duty, had only minutes to decide whether or not the satellite data were a false alarm. Since the satellite was found to be operating properly, following procedures would have led him to report an incoming attack. Going partly on gut instinct and believing the United States was unlikely to fire only five missiles, he told his commanders that it was a false alarm before he knew that to be true. Later investigations revealed that reflection of the sun on the tops of clouds had fooled the satellite into thinking it was detecting missile launches. This event was turned into the movie The Man Who Saved the World, and Petrov was honored at the United Nations and given the World Citizen Award.

2) October 27, 1962: Soviet Sub Captain Decides to Fire Nuclear Torpedo During Cuban Missile Crisis
This may be the closest call of all – so far. During the Cuban Missile Crisis, eleven U.S. Navy destroyers and the aircraft carrier USS Randolph had cornered the Soviet submarine B-59 near Cuba, in International waters outside the U.S. “quarantine” area. What they didn’t know was that the temperature onboard had risen past 45ºC (113ºF) as the submarine’s batteries were running out and the air-conditioning had stopped. On the verge of carbon dioxide poisoning, many crew members fainted. The crew had had no contact with Moscow for days and didn’t know whether World War III had already begun. Then the Americans started dropping small depth charges at them which, unbeknownst to the crew, they’d informed Moscow were merely meant to force them to surface and leave. “We thought – that’s it – the end”, crewmember V.P. Orlov recalled. “It felt like you were sitting in a metal barrel, which somebody is constantly blasting with a sledgehammer.”

What the Americans also didn’t know was that the B-59 crew had a nuclear torpedo that they were authorized to launch without clearing it with Moscow. Indeed, Captain Savitski decided to launch the nuclear torpedo. Valentin Grigorievich, the torpedo officer, exclaimed: “We will die, but we will sink them all – we will not disgrace our Navy!” Fortunately, the decision to launch had to be authorized by three officers on board, and one of them, Vasili Arkhipov, said no. It’s sobering that very few have heard of Arkhipov, although his decision was perhaps the single most valuable contribution to humanity in modern history. PBS made the movie The Man Who Saved the World about this incident.

1) The incidents that keep happening
These are only a sample of over two dozen close calls that we’ve catalogued in this timeline, and there are almost certainly more, since some have been revealed only decades later. Also, although most nuclear incidents were reported by U.S. sources, there’s no reason to believe that the opposing superpower had fewer incidents, or that there have been zero incidents in China, the UK, France, Israel, India, Pakistan or North Korea. Moreover, near-misses keep happening. Although some argue that the superpowers should keep their current nuclear arsenals forever, simple mathematics shows that nuclear deterrence isn’t a viable long-term strategy unless the risk of accidental nuclear war can be reduced to zero: Even if the annual risk of global nuclear war is as low as 1%, we’ll probably have one within a century and almost certainly within a few hundred years. This future nuclear war would almost certainly take more lives than nuclear deterrence ever saved. If you want to reduce the risk of accidental nuclear war, please help raise awareness by sharing this timeline.