Wednesday, November 23, 2016

GPS Jamming

We’ve discussed the military’s overdependence on GPS guidance (see, "GPS - The Navy's Addiction") and briefly noted the adverse effects if the GPS signal could be jammed.  US guided weapons are heavily dependent on GPS as their primary guidance mode.  While other modes are available, they are far less accurate.  This is disturbing because accuracy, or precision guidance, was the cornerstone of the Second Offset Strategy, and the loss of that capability would be devastating.  We’ve justified our reduced numbers of ships and aircraft in large measure by the claim that our weapons are so much more accurate than they were that we no longer need as many.  This is foolish to the nth degree but is, nevertheless, the basis of the rationale for reduced numbers.  If our weapons could be rendered significantly less accurate and we have lesser numbers compared to our enemies, we would be in serious military trouble!

Can a GPS signal be jammed?  Apparently, it’s quite easy.  GPS signals operate at very low power and over a very narrow frequency range – the ideal combination for jamming or disruption.

“GPS signals, transmitted at low power from distant satellites, are uniquely susceptible to jamming.” (1)

“A 1-kilowatt jammer can block a military GPS receiver from as far away as 80 kilometers (50 miles). A Russian company recently marketed a 4-[kilo]watt jammer that can deny a standard GPS signal within up to 200 kilometers (125 miles).” (1)

North Korea has reportedly jammed GPS signals over South Korea on over 100 occasions.  The jamming reportedly affected aircraft, ships, cell phones, and cars.

North Korea reportedly purchased truck-mounted GPS jammers from Russia with a range of thirty to sixty miles, and in 2011 was reportedly at work on even longer-range jammers.” (2)

Some weapons offer alternative navigation modes such as Terrain Contour Matching (TERCOM), Digital Scene Matching Area Correlation (DSMAC), and Inertial Navigation (INS), however, these have significant drawbacks and limitations.  Two of those options require the weapon route to have been pre-mapped which is not always possible.  INS is inherently inaccurate.

Supposedly, military GPS signals are more resistant to jamming and disruption but I’ve been unable to find any authoritative information on that.

As we ponder GPS issues, here is an example from personal experience.  Not too long ago, I had the pleasure and privilege of touring a Cyclone class PC that was docked at a large US city.  I noticed that the ship’s GPS navigation system showed the vessel to be about 30 miles inland, in the middle of a park.  Screwed into the bulkhead next to the ship’s system was a commercial GPS navigation display from a well known outdoor camping gear store.  I asked the crew about it and was told that they had used their own money to purchase the commercial unit because the ship’s system was never right.  They simply used the commercial unit which was always dead on.

I don’t know how widespread accuracy and reliability issues are with military GPS units but I’ve got to believe this was not an isolated incident.  If we have significant numbers of ships using commercial units then we’ve made ourselves extremely vulnerable to GPS jamming and disruption.  This also suggests that we need to relearn how to navigate without GPS.


(1)MIT Technology Review website, “How Cruise Missiles Would Beat GPS Jammers in Libya”, Christopher Mims, 20-Mar-2011,

(2)Popular Mechanics website, “North Korea Is Jamming GPS Signals”,  Kyle Mizokami, Apr 5, 2016,


  1. The future may be Quantum positioning system, it looks viable system to replace the GPS if the R&D funding is found.

    Submarines cannot use GPS as signal will not penetrate water and so the subs rely on the relatively inaccurate INS, can easily be 1 KM off from true position when resurfaces. So research ongoing for a more accurate navigation system based on the the Nobel Prize in Physics Prize of 1997 for development of methods to cool and trap atoms with laser light.

    The New Scientist article May 2014 describes UK research in quantum positioning system based on "lasers can trap and cool a cloud of atoms placed in a vacuum to a fraction of a degree above absolute zero. Once chilled, the atoms achieve a quantum state that is easily perturbed by an outside force – and another laser beam can then be used to track them. This looks out for any changes caused by a perturbation, which are then used to calculate the size of the outside force"

    "It’s not a done deal yet, though, because the accelerometer can’t distinguish between tiny gravitational effects and accelerations caused by a vessel’s movement. If the submarine passes an underwater mountain whose gravity attracts it to the west, that feels exactly like an acceleration to the east,This means that very good gravity maps will be required to navigate correctly.”

    “The submarine does not need to know its position in metres and centimetres,but a projectile like a missile or shell might.”

    "Future generations of the technology are likely to make their way into everything from cars to our smartphones."

    1. Yer I would been following this with interest since that article broke. [ It went out on a RN sub around that time. ]

      However the entire project has gone black. So I assume its working well.

      Problem is Quantum-INS is only 1000 times more accurate, and over time this still needs updating.

      This could be the answer for hypersonic \ short range weapons ( as INS navigation goes innacurate relative to time ).

      But its no good for the launching platforms, which could have spent days in transit \ battle.

      I think the worse threat is not GPS jamming, but GPS spoofing ( as is theorised the Iranians did to that RQ170). Convincing a GPS receiver its hearing different GPS satellites and is therefor somewhere else.

      Its actually frighteningly simple it seems.

      Do this and we will end up shooting at ourselves !

    2. As for quantum INS, just because it's gone black doesn't mean anything except that it has gone black.

      There have been programs that have been classified before to hide serious mismanagement of taxpayer funds before. It's shameful, but it does happen.

      We don't really know for sure.

    3. I believe the Y code and the new M code are cryptographicaly secure against spoofing.

      I've seen different claims about Iran and RQ170, really have no idea what happened there. The Iranian's claim jamming + spoofing, but it would be a really poor design decision if the drone fell back to the spoofable signal if the secure one was jammed.

    4. "I believe the Y code and the new M code are cryptographicaly secure against spoofing."

      That's hilarious! Every major company that's been hacked believed their system was secure.

    5. Perhaps, but that says little about the security of key national security assets. Spoofing a SAASM GPS signal is the equivalent of forging encrypted messages; an adversary that could do that would also be able to, for example, fake IFF responses or send messages to subs that authenticated as from COMSUBxxx.

      There's some stuff that I haven't been able to learn anything about that is supposed to prevent a captured SAASM (secure GPS) receiver from being reverse engineered. No idea how well that works. Other than that, I think the only way for an enemy to defeat the anti spoofing would be to compromise the part of the Air Force that uploads codes to the GPS sats.

      Of course, there's an easy way to defeat the anti spoofing: "Screwed into the bulkhead next to the ship’s system was a commercial GPS navigation display from a well known outdoor camping gear store"

    6. GPS signal encoding is not my forte but, as I vaguely understand it, the previous military signal was encoded (the new version is supposed to be even "more coded") and may have been hacked by Iran. That's a claim that has yet to be confirmed, of course. However, the fact that the military felt the need for "more code" suggests that they realize that there is no such thing as secure code/signals. There are only two types of code/signals: those that have been hacked and those that will be hacked when someone cares enough to be worth their time to do it.

      Recall the results of the Pentagon's hacking challenge when amateur hackers generated a hundred unique hacks in just a few days against a supposedly secure network? Imagine how much worse for us, and easier for the hacker, if professional, state-sponsored Iranian/NK/Chinese/Russian military hackers who's only job it is is to hack the US military were to attempt the same thing (and they probably do on a daily basis).

    7. AFIK, the new M signal is supposed to be quicker to acquire and harder to jam. The current P(Y) signal can take a very long time to acquire (maybe why your friends on the Cyclone used a commecial unit?).

      In terms of hacking, I see your point. I do believe the core "crypto package" in GPS is secure, but all of the ancillary systems around it could be vulnerable. One would hope that the people who manage GPS keys practice good IT hygene.

      The reverse engineering thing is scary. Compare the old (romantic? real?) story where a Captain's last duty was to destroy the code books, with today, when there's a code book in every munition.

    8. "I do believe the core "crypto package" in GPS is secure"

      Venturing outside my expertise here but what the heck ...

      Nothing is secure. Bear in mind that the purpose of the core code is to encrypt the signal at the transmission end. Well, any signal can be intercepted - that's fairly easy. The question is whether the encryption can be decrypted. The answer to that is yes, given enough time and effort any encryption can be cracked. So, the core code is good only until someone cracks the encryption. Sure, we'll use all kinds of tricks to make that process harder but, ultimately, any encryption can be decrypted.

      There's also the alternative approach of "simple" jamming (disruption) of the signal. It doesn't matter if the signal is encrypted if you can jam it so that the receiver can't pick the signal out of the background noise.

      Another disruptive technique is to inject a false signal into the transmission. No need to jam or decrypt if the receiver can be made to think that a spurious signal is the real one.

      And, of course, there's good old fashioned shooting down of the GPS satellite.

      I'm sure that there are other methods to deny a GPS signal as well.

      The overall point is that GPS is a pretty insecure system which is vulnerable to multiple methods of denial. We need to wean ourselves off of our dependence on GPS and make sure that we have multiple backup modes/methods of navigation all the way "down" to maps and compasses and dead reckoning (the technique used by Marine LAVs for desert navigation in Desert Storm!).

  2. You are right about INS innaccuracy, but if you can set up dec stations while GPS reception is good and use them after you lose GPS if you know where you will operate.
    Yes I realize this does not work if you are conducting an assault on a place you have not been before, but maybe you can send a recon team to set these up ahead of time.

    Is there a ship equivalent to a survey dec station?

  3. Sorry SurfGW, Ben Oliver is correct, cheap quantum mechanics based INS is already maturing and is meant to be hyper accurate. It will not likely replace GPS, but will act as a supplement, and likely take over should a logic machine start seeing discrepancies between the 2 inputs. Ideally you want a 3rd input and the input with the largest discrepancy is dumped, but, not sure what the 3rd one would be just yet.

    CNO, whatever else happens, the march is ever on, not back, we'll never go back to reading maps to navigate, those days are gone. So, not arguing the vulnerabilities of modern tech, just saying, we wont be going back to maps and stop watches.

    1. "we wont be going back to maps and stop watches."

      You've completely missed the point of all my previous posts and comments about navigation. When have I ever stated that we should dump all our GPS/INS/radar/radio beacon/whatever forms of navigation? The answer is never. Now that we're straight on that, I'll explain, yet again, what I've been saying all along.

      We need to eliminate our DEPENDENCE on GPS and whatever other forms of electronic navigation that can be disrupted. Our dependence has made us unable to function when our electronic methods are cut off, as they inevitably will be in war. We need to be able to navigate via maps, compass, and dead reckoning, AS A FALLBACK METHOD. We can't just fold up and go home because an enemy figures out how to jam or spoof our GPS. THAT IS NOT THE SAME AS SAYING WE SHOULD ABANDON ALL ELECTRONIC NAVIGATION. Have I been clear enough, now?

      The Aegis cruiser USS Port Royal ran aground when their GPS failed and no one knew how to navigate by any other means.

      When a soldier loses his GPS mapping, he needs to know how to navigate by map and compass.

      As an analogy, despite all our modern, long range rifles, artillery, air power, missiles, and nuclear weapons, we still teach hand-to-hand combat because, inevitably, the need still arises in war. So, too, the ancient (and unjammable) means of navigation must be learned. Inevitably, at some point in combat, ships, aircraft, and soldiers will, indeed, have to go back to "maps and stop watches" and we'd better know how to use them.

      This is not a point I'll debate further.

  4. I think that the US is operating on many dangerous assumptions that won't prove true.

    If North Korea can acquire the technology to jam GPS, one is forced to conclude that a modern military can do so with substantially greater ability.

    Training should reflect that, as should all assumptions in war games - the enemy will try to jam GPS.

    It's like the US is a team of sports that instead of fighting in the big leagues, has been mostly facing little league opponents and assumes that it will always be like that. War is not sport, and the analogy is imperfect, but there similarities are striking.

    1. "one is forced to conclude that a modern military can do so with substantially greater ability."

      Quite right and the lessons are plainly visible. The Russians are putting on a clinic in electronic warfare in Ukraine and, essentially, parading their equipment for us to see. All we have to do is pay attention and learn from it and yet we refuse to conduct full electronic warfare against ourselves in our routine training exercises.

    2. Maybe the (rather naively) think that they will always be able to fight Islamic Fundamentalist groups.

  5. A 4-kilowatt jammer would make a juicy target for an anti-radiation missile.

    1. If they have more jammers than you can have missiles, then it still might not work out very well.

    2. A HARM missile costs around $1M. I'm guessing a 4-KW jammer might cost a few thousand. That's not a good trade. An enemy can manufacture far more jammers than we can missiles.

  6. In addition to that, I do believe the NVA had a system in place where they could alternate radar stations to maintain target acquisition while reducing the risk from wild weasel missions. So theoretically, they could have several jammers alternating to do the same thing.