North Korea’s GPS Jammer Brigade

North Korean soldiers look in from outside the UN Command Military Armistice Commission meeting room on July 15, 2011 in Panmunjom, South Korea.

BANGKOK, Thailand — It’s among the Pentagon’s worst-kept secrets. GPS satellite signals, relied upon by military aircraft, warships and troops on the ground, can be scrambled with a $30 jammer off eBay and a bit of tech know-how.

Now it appears that North Korea, determined to drive U.S. forces off the Korean Peninsula, may have successfully jabbed at this Achilles’ Heel. Despite Pentagon denials, South Korean military reports contend that covert jammers in the North Korean hilltops likely triggered a U.S. spy plane’s “emergency landing.”

“It’s a wake-up call,” said David Last, a British GPS specialist and University of Wales professor emeritus who has consulted with South Korean officials.

Cheap, effective and sold on the Internet, GPS jammers are ideal for tech geek terrorism. Experts warn that a few dozen jammers, strapped to remote control planes and launched over a major city, could sow plenty of panic: disrupting ATM withdrawals, air traffic controllers, ambulance routes and cell phones.

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Weaponized GPS scramblers prove attractive to outgunned armies like North Korea’s because they wreak lots of confusion on the cheap. “It’s difficult for your enemies to do anything about them,” Last said. “It gives the attacker a considerable advantage for a very modest outlay of fortune or effort.”


We may never know for sure. The Pentagon, through an anonymous source speaking to Reuters, insists it never happened.

South Korean military documents, obtained by the Seoul media, tell a different story. A military report to lawmakers details a U.S. military RC-7B propeller plane, outfitted with surveillance gear, ending its flight near the North Korean coastline early after jammers overcame its GPS equipment.

The alleged “emergency landing” took place in March, when the U.S. and South Korea staged war games as a show of force for rival North Korea.

Ruler Kim Jong-Il’s regime deplores these routine drills, which ready warships, fighter jets and tens of thousands of troops along the border. Government statements call South Korea the “puppet warmonger” of the U.S., intent on “madcap joint tactical maneuvers.” Both Koreas consider their 1950-53 war to be technically ongoing.

The totalitarian regime is particularly mindful of U.S. surveillance planes that, according to statements, “indicate that the U.S. is always watching for a chance to make a surprise attack ... behind the curtain of dialogue.”

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Last year, North Korea vowed to end U.S.-South Korean war games with a “single strike” that would “wipe out the aggressors.” Several months ago, it renewed threats to “mete out merciless and strong punishment.”

Said a May propaganda dispatch: “We never make an empty talk.”

Bluster aside, North Korea’s jammers have so far proved merely aggravating to U.S. and South Korean forces. Scrambling GPS signals won’t cause planes to drop from the sky. Planes can still establish their position with radar.

A more-worrisome scenario could occur during all-out warfare. Bombs commonly used by the U.S. Air Force -- called Joint Direct Attack Munitions -- rely in part on GPS for precision targeting. According to the Defense Department, jamming a bomb’s signal could cause it to miss its target by nearly 100 feet.

South Korea’s “weapons and navigations systems” have suffered multiple North Korean jamming efforts, according to Seoul-based newspaper Chosun Ilbo, forcing the military to hastily switch to radar tracking.

By drowning out GPS signals, sent from faraway satellites, with frequencies blasted from a much-closer range.

A GPS signal is “extremely weak,” said Last. “The satellite transmits no more power than a car headlight and does so from 20,000 kilometers out in space. If you shout at it from nearby, using a jammer of modest power, you will drown out the GPS signal and the receiver will lose service.”

The North Koreans are believed to possess a mix of old Soviet jammers, purchased roughly 10 years ago, and their own homemade equipment. These jammers on wheels are positioned in Kaesong province hilltops around the border for maximum reach, Last said.

South Korean military reports suggest the Kim regime may have acquired high-powered jammers that can scramble GPS receivers from 250 miles away.

The cheap Internet-sold jammers, favored by truckers hoping to avoid their bosses’ scrutiny, typically cover only a 30-foot radius.

But even these eBay-available jammers can wreak havoc. Air-traffic controllers at the international airport in Newark, N.J., were confounded last year by frequent signal disruptions during attempts to land planes with GPS.

It took several months to locate the culprit: the jammer of a truck driver who frequently drove past the airport’s GPS ground antenna.

According to a report by the U.S. agency overseeing GPS — the National Coordination Office for Space-Based Positioning, Navigation and Timing — the only “punitive action for the deliberate interference was to confiscate the jammer.”

Well aware of GPS signals’ frailty, the U.S. military almost always insists its systems have back-up navigational systems that don’t depend on GPS. Just before the Sept. 11 attacks, the U.S. transportation department released a report acknowledging jamming as a major threat to “banking, communications, data processing and internet enterprises.”

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“Ten years later, the threat is more widely understood, but relatively little has been done about it,” Last said.

The U.S. government’s GPS agency is adamant that commercial airliners “maintain alternative means of navigation” to prevent terror attacks. “The government is currently fielding new GPS signals that are more resistant to jamming,” according to the agency.

Far more vulnerable are the GPS signals used by police, banks, coast guard vessels and anyone with an iPhone. If North Korea’s jammer brigades can really scramble signals in a 250-mile radius, they could easily target nearby Seoul -- as could any group in any major city with trove of $30 jammers and a desire to stir panic.