Nuclear 201: Will You Be My PAL?

A guest post by John Donovan, the Armorer of Castle Arrgghhh (and Lizzie)

Nuke weapons design and policy are governed by the need for safety and control. PALs are a component of control.

What is a PAL? PAL stands for Permissive Action Link. The purpose of the PAL is not to prevent unauthorized use of a nuclear weapon by rogue elements of the US military command. We do that via the EMAS (Emergency Message Authentication System) and NRAS (Nuclear Release Authentication System) systems and the imposition of strict two-person control (at a minimum) at each step of the process.

Some of those processes can be longer than others, depending on whether the weapons involved are “first strike deterrent” weapons like the USAF ballistic missiles and the USN SLBMs (Submarine Launched Ballistic Missiles) or further down the chain like the manned bombers, cruise missiles and formerly, US Army tactical nuclear missiles and artillery. PALS are also distinct from
safeties. Safeties are intended to prevent premature or accidental initiation or partial initiation of a warhead.

PALS have a different niche.

NATO airbase, mid-sixties. NATO fighter-bomber, fully fueled and armed, sits on “strip alert,” pilot strapped in. A lone US Airman armed with an M1 carbine stands guard. He is literally the only thing standing between chaos and disaster should that non-US NATO pilot decide (or get told by his government) to light up his jet and go bomb a target. Soviet or not. (1)

US Army Warhead Detachment, Mid-70s. NATO ally army trucks and some tanks roll up to the Detachment’s gate. The purpose of the detachment is to secure and maintain nuclear warheads (missile or artillery) stored in NATO nations that are there for either US units, or, upon authorization, NATO
units. Tensions are erupting between the ally and another nation and signals intelligence indicates that the ally’s generals have been talking to each other about taking some of the warheads to use as a lever against the other belligerent. While the confrontation at the gate never happened, the conversations did. (2)

Hey, NATO Ally – are you my buddy, my pal right now? No? That is why have PALs. To prevent unauthorized people from using US-provided nukes without express authorization from the President of the United States. The problem with both of those scenarios is that besides being scary as hell, it was (and still is) contrary to US law about control of US nukes, i.e., only we could give release, no one could take one of our weapons and use them unilaterally. Only we get to do that.

Yet, we gave nuclear-capable weapon systems to allies – the Nike-Hercules air defense missiles, various US Army tactical missiles like Honest John, Lance, and Pershing, and 155mm and 203mm nuclear artillery projectiles. And many NATO aircraft were nuke-delivery capable. And all that had to be scattered around Central Europe so that those nations could quickly employ them if things got ugly on the North German Plain and the rolling hills of Bavaria along the Czechoslovakian border. Same was true of bombs, and NATO aircraft on Quick Reaction Alert (QRA).

We needed something better than the Airman 1st Class-Mounted M1 Carbine Nuke Weapon Disabler. There are four types of PALs (at least that are acknowledged publicly these days) that are variations on a theme. They are either electrical/digital and integral to the weapon, buried inside where it is hard to get to them, and they interfere with the arming/initiation process until unlocked from an external code transmitted to them, or they are like combination locks that must be unlocked with a code thoughtfully provided by a two-man US warhead team acting under orders with the codes received via the NRAS system. Mechanically removing them will take time, and, most likely, render the warhead inoperative.

Giving hopefully cooler heads time to intervene. A balance between the profound need to control release and the tactical realities of modern combat
“Bypassinag a PAL should be, as one weapons designer graphically put it, about as complex as performing a tonsillectomy while entering the patient from the wrong end.” (3)

Acknowledgements and further reading, if you want further unclassified details.

A useful unclassified and easy-to-read discussion of PALs.
Steven M. Bellovin Permissive Action Links ( A useful unclassified and easy-to-read discussion of PALs.
A drier, more technical discussion of both Safety and Control. Subscription to the Bulletin is required to access the archived articles.
U.S. Nuclear Weapons Safety and Control Features To cite this article: (1991) U.S. Nuclear Weapons Safety and Control Features, Bulletin of the Atomic Scientists, 47:8, 48-49, DOI: 10.1080/00963402.1991.11460025

(1) Stein, Peter and Feaver, Peter. Assuring Control of Nuclear Weapons. University Press, 1987
(2) Reed, Thomas C. At the Abyss: An Insider’s History of the Cold War. Presidio Press/Ballantine Books,
(3) Caldwell, Dan and Zimmerman, Peter D., “Reducing the Risk of Nuclear War with Permissive Action
Links”, in Technology and the Limitation of International Conflict, Blechman, Barry M., ed., Johns
Hopkins Foreign Policy Institute, 1989.

Acknowledgement: The author wishes to acknowledge the sharp eye and excellent editorial instincts of Lizzie, a feline of great discernment. Not only did she keep him company and offer encouragement, she added stray characters and deleted random paragraphs to test this scribbler’s skill. Sic Semper Felinus.

Acknowledgement II: This old wolf wishes to thank John for coming out of blogging retirement, as it were, to add to the Nuclear 201 series and to Lizzie for her contributions as well.



Nuclear 201 Posts In Order

Nuclear 201: Some History

Nuclear 101 Posts In Order:

Nuclear What?

Nuclear 101: Weapons

Nuclear 101: Delivery

Nuclear 101: Now What?

Nuclear 101: Targeting

Nuclear 101: Scenarios

Nuclear 101: Survival

Some Quick Thoughts


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17 thoughts on “Nuclear 201: Will You Be My PAL?”

  1. Mr. Wolf (so-to-speak) – can you tell us all, please, exactly what makes a bomber ‘nuclear-capable’? Or is this just a term that the MSM uses when when they want to get us all extra-scared about some situation?

    1. Heh. It generally is the latter: a term used when they want to scare people. One author I can think of used to always use that phrase, then admit right at the end of the story that it meant it could carry a nuclear weapon. This was in “Russian nuclear bomber approaches US coast” type stories. It was almost always a Bear, which could carry nuclear weapons but was primarily used for long-distance recon since it was prop not jet and could stay up for what seemed like forever. Heck, a Piper Cub could technically be nuclear capable, if you stuck a small tactical device in it. That said, on our end, the plane had to be capable of carrying the device and supporting PAL and/or other safeguards to be nuclear capable. Most Russian bombers and fighter-bombers are technically nuclear capable as they can carry various ranges of nuclear devices. Which is why I tend to consider the news reports that breathlessly push “nuclear bomber” or “nuclear capable plane” to be going for sensationalism.

    2. John is absolutely correct when it comes to our side. What makes a plane (or other) nuclear capable is the “fiddly bits” as it were. It is true for any nation/group with a brain, as it is generally considered a good idea to do things so a hot-head can’t go do something stupid.

      The Soviets, now Russians, are believed to have similar in regards strategic weapons. Where the debate has been, let’s say somewhat robust, gets into how far that extends to tactical weapons. Their doctrine envisions the use of special weapons on the local, and a number of their aircraft are purported to be able to carry such devices. Not to mention rockets, artillery, and related.

      Where this breaks down is with some of the newer nuclear powers, and groups that are working to become nuclear armed. One hopes that they include safeties, but one would be wise not to count on it.

      Again, when it comes to Russian aircraft, quite a few are technically nuclear capable. The use of “nuclear” or “nuclear capable” plane in the media is, however, most often a scare tactic given the large number of Russian assets that are technically nuclear capable.

  2. Not all aircraft are capable of dropping/firing nuclear weapons. They have to have, among other things, suitable software, and the needful ability to make suitable data links, both in terms of external coms and internal, i.e., to the weapon itself. All them safeties. And the PAL…

    A “nuclear capable” aircraft is one the has the neccessary fiddly-bits” to be able to mount a nuke.

    A “nuclear-armed” aircraft is one that has one mounted.

    1. It’s not just ability to “mount a nuke.” It’s much more about the electrical interface than the mechanical interface.

      Nuclear capable aircraft have AMAC – Aircraft Monitor and Control Systems. This is the system that communicates with nuclear weapons. (Note there is a difference between bombs — aircraft plugs directly into each bomb, and cruise missiles — aircraft plugs into cruise missile which, in turn, communicates with nuclear warhead.) Non-nuclear aircraft (such as B-1) weapon stores interfaces are insufficient. AMAC is some of the “fiddly bits.”

      B-2, B-52, F-15, F-16, F-35 are nuclear capable. B-1, F-22 (and all other US) are not. B-21 will be. Navy quit the game a long time ago. Europe has some. The term to search for is DCA – Dual Capable Aircraft.

  3. IIRC Dr Stranglove has a good scene that shows both the NRAS card cracking and putting the release code into the PAL box. or at least the box that talks to the bomb PAL box

    Slim Pickens and James Earl Jones

    1. I have heard that the U. S. Air Force refused to cooperate with the director of Dr. Strangelove, because the USAF maintained that what happens in the movie could not possibly happen in real life. I also heard that the USAF was rather upset when they saw the mock-up of the bombardier’s station in the movie. It was a little too accurate, especially considering the set designer should have had no idea.

      1. As I understand it, the set designer had a couple of small, blurry photos of a B-52 cockpit from Life magazine. He used that, pictures of B-17’s, 707’s, and a bunch of educated guesses. And yes, USAF was not pleased.

  4. Back 40 years ago I was on a USAFE base. If you flew from that base toward Germany you had to cross water. I dated a nuclear weapons specialist. That’s just what it sounds like; someone trained to maintain the nuke part of a nuke weapon (some of the non-nuke parts, too, but I distinguish between someone who fixes say, a Minuteman missile, and the people who fix the warheads on top of the missile).

    Of course, the rule was that the USAF never confirmed, nor denied, the presence of nuclear weapons at any facility.

    There were two types of fighter aircraft stationed at the base. In case of tension with the Warsaw Pact, we expected other fighter aircraft to come over from the US.

    The two types permanently there both lacked the fiddly bits they would need to deliver nuclear bombs. This was not a huge hairy secret; one could look it up in Jane’s All the World’s Aircraft. And yet, we had nuclear weapons specialists on hand. They worked on stuff, too. I never knew what stuff, and I didn’t ask, but they did things.

    When they worked on things, two people from a short list had to be in the room (that list did NOT include the wing commander, I was told). If one had to go pee, another person from the list was summoned first, before the bathroom break.

    People on that list were watched. It wasn’t oppressive, but if a person started acting odd, or displayed symptoms of depression, or expressed a burning desire to visit the Soviet embassy, it was noted, and questions were asked. People lost their Personnel Reliability Program certification for behavior the authorities didn’t like.

    I had a security clearance equal to hers, which was high. Mine was higher than my commander, which he didn’t like, but tough. Despite having that clearance I would not have been allowed within 50 yards of her work area.

    1. Of course, the rule was that the USAF never confirmed, nor denied, the presence of nuclear weapons at any facility.

      for the Navy it’s easy. If the weapons storage facility is guarded by Marines, it has nukes, else rentaguards

    2. ” People lost their Personnel Reliability Program certification for behavior the authorities didn’t like.”

      I ran an Army PRP list in support of FRG located FA and ADM missions. I once had to visit my boss’s boss’s boss. a BG, to tell him that I had taken his subordinate, my Boss’s Boss (Bde Cdr) out of the nuke chain of command temporaily, on advice of my Doctor advisor because the Bde Cdr had been in an auto accident and been unconcious. The withdrawal lasted 6 months.

  5. A simple but important distinction:
    The purpose of safety systems in nuclear weapons is to prevent ACCIDENTAL (always unauthorized) nuclear yield.
    The purpose of PAL is to prevent INTENTIONAL unauthorized nuclear yield.
    Both while allowing intentional AUTHORIZED nuclear yield.
    This difference in purpose results in them being handled very differently from each other.

    Historically, nuclear safety details have been unclassified, in part to allow the widest possible scrutiny to find “mistakes.” (Since 9/11 the risk/benefit considerations have changed, and there has been a move toward restricting more design and operational details.)

    In contrast, PAL has always been highly classified. While a Q clearance certifies the holder has sufficient clearance, it does not indicate “need to know – NTK.” Access to non-trivial PAL details is controlled by formal NTK groups — Sigma 15 – for PAL design; Sigma 14 – for PAL vulnerabilities. To access such information a person must have Sigma 14/15 AND specifically approved NTK for each program that person is allowed access.

    Note there is a separation between DOD and DOE/NNSA on nuclear weapons knowledge. Operators do not need to know design details for a PAL. And especially we do not want operators with hands-on access to know how to bypass PAL. Relatively few people in DOD have Sigma 15 and even fewer have Sigma 14. Sigma 14 is generally not allowed on DOD computer systems including those above SIPR.

  6. In the context of this article, the main distinction between USAF ICBMs/Navy SSBNs vs aircraft weapon systems is not “first strike” or not. The distinction is driven by the need to have coded control on weapon use and how it needs to be different for long range ballistic missile than for aircraft.

    An ICBM/SLBM launch would be alarming to our competitor nations. They might do something rash in response. We don’t want an ICBM or SLBM ever launching (without authorization). So we incorporate coded-control into the missile launch systems. Keep the missiles in the hole.

    In contrast, aircraft fly around all the time. It is not feasible to apply coded control to the aircraft itself. Instead we apply coded control to the weapons themselves.

  7. bit of trivia. DOD ‘owns’ no nukes. The NNSA signs them over on a hamd-receipt. As long as, when you push the test button, you get green lights, you are gtg. If one breaks you send it to the NNSA shop for repair. Yes, DoD can change batteries and swap a few things.

    So after WW3, some AF officer is going to show up at NNSA and ‘clear’ his hand receipt by showing BDA photos of a glassy Moscow hole, etc.

  8. LW,

    You might consider a post on the 2008 Minot debacle, as an example of multiple chained failures of the nuke control system

    1. heh. I probably should do a nuclear scare-the-schiff out of people series once this is wrapped up. Still amazed at how lucky we’ve been overall…

      1. “Luck is the residue of preparation.” — Jack Youngblood

        Yes, we have been lucky. We could have been unlucky. But it wasn’t just a random roll of the dice. A lot of thought and effort goes into our lack of major disasters (nuclear yield, well-beyond Damascus or Palomares) to date. And we try to learn from experience and improve.

        Not flying bombs around 24×7 helped our odds a lot.

        Conversely, complacency, lack of attention to detail and normalization of deviance can bite us at any moment.

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