The Remarkable Mechanism That Secures Nuclear Weapons

In the early days of nuclear weapons, security measures were surprisingly basic. This video explores the fascinating history and development of Permissive Action Links (PALs), the sophisticated systems that now safeguard nuclear arsenals.

Timeline:
1940s-1950s: Primitive security measures
- Weapons kept partially disassembled
- No formal policy on custody, control, and proliferation
- Simple 3-digit combination locks introduced

1953: Missiles and Rockets agreements
- Defined roles of Atomic Energy Commission (AEC) and Department of Defense (DoD)

1961: Committees formed to study use control
- Special Warhead Arming Control (SWAC) Committee
- Safety Steering Group
- Joint Command and Control Study Group Project 106

August 1961: Secretary of Defense requests AEC to create permissive links for NATO weapons

June 1962: President Kennedy issues NSAM 160
- Mandates PALs on all U.S. nuclear weapons in NATO countries

How PALs Work:
1. Isolation: Critical components enclosed in "exclusion region"
2. Incompatibility: Designed to prevent accidental activation
3. Inoperability: "Weak links" render weapon inoperable in extreme conditions

Key Components:
- Stronglinks: Rugged electromechanical devices controlling weapon arming
- Energy control elements: Create pathways into exclusion region

PAL Categories:

Category A (1960s):
- MC1541 coded switch (5-digit code)
- Complex operation, took 30 seconds to 2.5 minutes
- Required multiple support equipment pieces

Category B (mid-1960s):
- MC1707 coded switch (4-digit code)
- Faster operation, cockpit control possible
- Fewer wires, parallel unlocking for multiple weapons

Category C (mid-1970s):
- Extended Cat B capabilities
- 6-digit code
- Introduced limited code attempt lockouts

Category D (1975):
- First microprocessor-based PAL (MC2764)
- Multiple Code Coded-Switch (MCCS) concept
- 6-digit codes for various functions (arm, train, disable)
- Interfaced with MC2969 Intent stronglink
- Anti-intrusion sensors, some self-powered

Category F (mid-1980s):
- 12-digit code system
- Advanced features: code-driven disable modes, emergency stops
- Variable yield adjustment via code
- Encryption in the arming process

Key Developments:
1980s: Modernization efforts
- Second-generation stronglinks: detonator and dual magnetic
- Improved reliability and reduced manufacturing costs

1997: PALs installed on all U.S. nuclear devices
- U.S. Navy last to receive them

2001: PAL Code Management System (CMS) deployed
- End-to-end encrypted method for re-coding weapons
- MC4519 MCCS Encryption Translator Assembly

2004: CMS fully implemented across all PAL systems

Future Developments:
- Ongoing miniaturization and ruggedization
- Micromachining technologies for mm-sized components

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#NuclearSecurity #PermissiveActionLinks #MilitaryHistory #DefenseTechnology #NuclearWeapons #ColdWar

[rekire___]

Wait till lockpicking lawyer said "inexcusable design flaws"

[daveb]

Im surprised he didn’t talk about the time a quarter of the entire nuclear arsenal had to be rebuilt because neutron absorbers used as safeties ended up crumbling and getting stuck in the cores.

[patrickvolk]

Nuclear weapons are designed to be two-point safe. Two points of failure will not allow a nuclear detonation. There also is another concept, which sounds scary; instead of fail-safe, it is fail-deadly. A failure will render the weapon unusable, and not necessarily in a manner where it can be reused. A fizzle is a possible fail-deadly outcome, which is essentially a dirty bomb without the nuclear payload going critical. There is some environmental checks, where the warhead doesn't arm unless it is launched, reaches space, and achieves a ballistic trajectory (e.g. you can't take a warhead and detonate it on your own).
They also have training and tactical settings.

[VenomU]

There is a ton of stuff I would like to say here. However, I don't want to spend the rest of my life in jail. But there is one correction I can make. "weak links" (as you term it) do not render a weapon inop. Weapons are stored "inop". "Weak links" simply prevent a P1 detonation. (P1 - Primary explosive, layer 1)

[michaelimbesi]

7:25 This section is easily the most beautiful and peaceful video segment ever produced on the functioning of atomic weapons.

[uriituw]

These videos are among the most well researched and comprehensive on YouTube.

[ARKSYN]

Although not the purpose, this video is the best explanation I've seen for how nuclear weapon detonations work on a mechanical level. I never knew how the explosion was actually triggered until now.

[dbblues.]

Once you mentioned being able to unlock weapons from a cockpit, I immediately thought of the scene in Dr Strangelove when Slim Pickens is arming the bombs in his B52

[brunonikodemski]

It is believed by many who were involved in Project Azorian, that the K129 Russian submarine which was partially recovered by the US, was attempting to make a nuclear strike toward US territory, via one of its R21 missiles. The only relevant target would have been the Hawaii naval bases, or possibly Alaska. Because the warhead exploded on one of the missiles, causing a large hole in the submarine, it is conjectured that one of the launch officers decided to enter an incorrect enabling code to the warhead, which caused it to asymmetrically, as a result of their PAL link deciding that not properly enabled, and decided to safe itself. Unfortunately, Azorian was not able to bring up the other two missiles, but did bring up some torpedos and mechanical engine structures. As such, no one will ever know the true cause of this explosive event. The Russians did go back to that location, after it became known that there were nuclear assets still remaining there, but to my knowledge, they have never released information about what they dredged up. Theoretically, there may still be two nuclear missile warheads and one nuclear torpedo remaining at that site. Some of our company employees were part of that project.

[MrWATM]

For decades all our nuclear PAL codes were all set to straight zeros because the system was too complicated.
Seriously.

[petersmythe]

Douglas MacArthur: "can I have use a nucle-

Everyone: *absolutely not*

[christopherleubner]

The actual lock is a still electromechanical.its a BCD electromechanical relay on the AF&F control board. The device is a little gold box similar to the size of one of the CP claire DIP reed relays. It has a small mechanism similar to the type you would expect in a combination lock that is driven by a tiny solenoid motor. If the correct code is entered the motor pulses allign the wheels to activate a switch. If all is good then the switch pops a nonrecindable thermal delay fuse relay that enables the system to arm. Once armed the only way to cancel is to use the destructive command disable. The switch must also be pulsed to the correct position fast enough that the disable relay doesnt fire. If this happens the nuke must have the PAL control module and the EF&F board must be replaced. Both the single shot relays look like glass top TO3 transistors. All of this stuff is potted in a nondescript epoxy block buried deep inside the forward section of the canned subassembly. This would make it extremely difficult for someone take apart the device, hotwire it, then reassemble as a usable weapon.

[woodwaker]

I found this very interesting. I was in the USAF 1969-1973 as a crypto maintenance tech. After school for 1 year I was assigned to Offutt AFB which was SAC HQ and I maintained the Crypto gear in the underground command center as well as the many communication centers. I was able to see the machine that encoded the missile coordinates that were fed into the ground based systems. Lots of changes since then.

[artysanmobile]

It was the precision of capacitive discharge that made nuclear weapons possible. No other mechanism could deliver the needed energy with temporal accuracy.

[rael]

"This was in the 80’s, and used 6 digits. "
One time when I was in the AF someone actually messed with the coded switch on one of our bombers. The thing was always just sitting special protection. Anyone could touch it or ....whatever. But we all understood that doing so would be a quick trip to Leavenworth.
day I get a tap on the shoulder and told to immediately report to such and such office WITHOUT DELAY. It was the office of the O.S.I. Office of special investigation. The Air Force equivalent of the FBI. They grilled me for several minutes. They said they knew I did that I knew who did it. DID WHAT ????
After maybe 45 minutes I think they became convinced that I didn't know my answers matched my actual whereabouts on the day of the incident. The incident was that someone had dialed in SACSUC ....(or something to that effect) on the dang coded switch. It started a X storm, I can tell you. We never heard the end of that.

[Awesomes]

I recommend watching any and all of the Sandia videos - there are some stellar ones with dozens of the most influential people of the Cold War and after.

[frontier]

The Million Dollar Question is: Could the Lockpick Lawyer crack this?

[socal]

The guy who designed the Nestle Purina plant near our town is a semi-retired, old-school, engineer. This plant makes 3 kinds of cat food and takes up probably 100+ acres. It looks like a car manufacturing plant, it's that big. He's stayed in our rental a few times because he gets called down to re-design parts of the plant to new methods of production. He says today's young engineers aren't able to adapt and think outside the box so he's taken out of "mothballs" to keep the plant going. Do you think today's engineers could even replicate what these guys did back in the 50s-80s? I'm doubtful now.

[blacklistnr]

Cool video, but by about the half-way point the word bag of { permissive, action, strong, link, system, category A/B/C/D/E/F, control } became just funny noises

[Zardox-The-Heretic-Slayer]

next gen nuclear weapons will require you to input an impossible to read captcha to arm it and a subscription to change the yield.