Learning How A Nuclear Missile Stays On Target

In 1962, unlike today, most things didn’t have computers in them. After all, the typical computer of the day was a fragile room-sized box that required a gaggle of high priests to service it. But the Minuteman I nuclear missile was stuffed full of pre-GPS navigation equipment and a computer. In a few years, by 1970, the Minuteman III could deliver a warhead 13,000 km with an accuracy of 200 meters. Each one cost about a half million dollars, but that’s almost five million in today’s money. [Ken] takes on a very detailed tour of the computers and avionics that were nothing short of a miracle — and a highly classified miracle — in the 1960s.

The inertial navigation relied on a gyroscope, which in those days, were large and expensive. The Minuteman I required alignment with a precise angle relative to the North Star which naturally wasn’t visible from inside the silo. By the time Minuteman II arrived, they’d figured out an easier way to orient the missiles.

The name Minuteman, by the way, came from the weapon’s ability to launch in a minute. The gyros ran, more or less, all the time, and the solid-fuel rocket was always ready to go.

D-37 Computer

What really interested us, though, was the onboard computer. There was a basic model, the D17-B, in the Minuteman I. Later missiles used the D-37 computer. The D-17B was made to fit in a rocket casing and used a serial CPU, presumably to reduce “SWAP” (size, weight, and power). That means the 24-bit CPU was painfully slow, doing, at best, 12,800 additions per second.

The computer had no RAM, but did have a “disk” which was really more like a magnetic drum — common at the time — flattened out. The D-17B was made with discrete transistors — lots of them. The D-37 actually used integrated circuits. There is a picture of a D-17B looking like half of a washing machine tub alongside a D-37, about the size of a serious oscilloscope of those days. Fun fact: the surplus D-17B computers were given away to universities and other organizations for use as a general-purpose microcomputer.

There’s a lot more in the post. Be prepared to spend some time reading and looking at the detailed pictures. While we know nuclear weapons are frightening, we can’t help but admire a radiation-hardened computer built with ICs and able to withstand the shock of a rocket launch built back then.

If you want your own nuclear bunker keyboard, we’ve seen one. If you want to administer a Linux system with virtual counter-rotating keys, that’s possible, too.

75 thoughts on “Learning How A Nuclear Missile Stays On Target

    1. Sounds like Dr. Seuss’s Cat In The Hat:
      “When you’ve mislaid a certain something, keep your cool and don’t get hot. Calculatus eliminatus is the best friend that you’ve got.

      Calculatus eliminatus always helps an awful lot.

      The way to find a missing something is to find out where it’s not. “

    1. If my fallible human memory serves me right, the Minutemen of old were also called that because they could be called up and be ready to defend their community “at a minute’s notice”. That is to say, very quickly because they kept their general gear in their home, so they could be ready to go the minute a courier carrying their orders passed by.

    2. Sure, but the play was they launched in a minute “like a Minuteman”. Same origin as they were “ready at a minute’s notice.” So I think it was a double meaning, but I don’t know that for sure. Ken’s stuff is meticulously researched, so I would imagine if he said that, there was a reason (and probably a footnote; I didn’t look). But I’m sure it was the human Minutemen who inspired the name but it applied because of the 1 minute launch. Remember these were deterrents so if it took an hour to launch that was an impossibly long time while the adversary was striking your targets.

    3. I remember a bunch of ranchers in the border between US/MEx calling themselves minutemen, giving all kind of troubles to the authorities, they were in the news long time ago , I was a kid so I don’t remember much details, (I should say I’m old so I don’t remember much details :)

      So I guess they are like: I remember when I was a minutemen but I don’t remember much details. Anyway.

  1. This gem from a fascinating read:
    “A nuclear blast has many bad effects on semiconductors and can cause transient errors.”

    …not to mention the effects on people, buildings, etc. [ironic grin] I wonder where Ken learned all this and where he got the hardware to analyse. The Government is extremely reluctant to declassify anything that has to do with nuclear weapons, and this page seems to reveal more than is customary. So probably all of it is obsolete and superseded by a completely different way of doing things, would be my guess.

  2. hey editor – not clear if “one” refers to the entire missile or only to the D-17-B computer.

    Each one cost about a half million dollars, but that’s almost five million in today’s money.

    1. Oh please. The rest of nature isn’t some paragon of pacifism. Humans will build whatever they can figure out how to build, because they are a curious and resourceful creature. And we managed to resist thermonuclear war despite having all the bombs, didn’t we?

          1. Will he succumb to the maddening urge to eradicate history? At the MERE PUSH of a SINGLE BUTTON! The beeyootiful shiny button! The jolly candy-like button! Will he hold out, folks? CAN he hold out?

        1. If you’d lived through the height of the world and cold wars, you wouldn’t dismiss so nonchalantly how great an achievement our current peace is. Paradoxically, the further we get from those generations the less hope we seem to have. They saw hell, then they hovered their finger over the button just enough so that the conflagration didn’t start again. And believe me, it would have.

          I just don’t like when humans are made out to be an uniquely evil creature. We are curious and talented, and that leads us to the management of great energies. I think altogether we haven’t done so bad.

          What do you think would happen if wasps had satellite-guided hydrogen bombs? And I like wasps, i leave them alone to build their nests and give them water while they languish through summer. Sometimes you’ve got to give moral indignation and doomsaying a break

      1. Point of order:
        The guidance system for the Polaris missile, developed by MIT, provided the basis for the Apollo guidance computer. Sure, I’m not going to argue that developing more efficient ways to kill people is better than educating, feeding, or healing all of them, but occasionally, technology developed for the military has other, friendlier uses.

        1. Occasionally?

          Quite regularly, actually. It’s the main path for public funding of R&D, and it led to medical advances, transistors and ICs, nearly all space technology, advanced in commercial aviation, and (briefly) standardization in manufacturing. Other side effects include improved rail and interstate infrastructure and the “conex” box shipping container that has made global commerce so lucrative.

    2. As others have said, human nature is what it is. Were it not for investment in military stuff, some other power and/or resource hungry humans would attack, take over whatever people consider to be theirs, and do other unpleasant stuff to the losing side. The deterrent effect, however, doesn’t always work.

      It is unfortunate that seemingly no substantial, purely defensive technology has been achieved. It is the way of (general) humanity to turn anything into a weapon: even something as seemingly benign as a Coke bottle (hint: it’s a movie reference).

      1. If human nature is what it is and it brings us into what the human life is and the state of things among humans, and we are conscious about it , what about transhumanism? so if being human is the root problem, why almost everyone scream in panic (specially Judeo-Christians) when transhumanism is bring into the table? Even in the movies we have this cliche of the hero “preserving what make us humans” or “no playing to be god” I think China is steps ahead in this field but even there there are barriers, taking note on Lulu and Nana now nearly 5 years old, as for June 2023 they were: “Well, living a normal, peaceful, nondisturbed life,” accordinf to Dr. He Jiankui.Mistakes will be made of course. But living beings make mistakes :)
        The second option as I see it is propaganda, you know change the human behaviour and ideology for a specific purpose but is so damn slow and obviously is not working.

      1. Lol. You really believe that? What else does the ex Soviet union really have going for them? Do you really think they let go of their last and best trump card?

        You believe the war news way too easily. Did you learn this from a YouTube essay? Come on engage your head

        1. Who is “they”. The ones making the plywood parade missiles? The ones moving the 5 working fighters to whatever base an official is visiting? Quote from ICBM manufacturer “We pretend to make warheads and the Party pretends to pay us.”

      1. ISTR reading all about how the military and various fought tooth and nail to stop us getting cryptographically secure stuff, the battles PGP, RSA, Diffie Hellman by government, the classification of secure ciphers as weaponry.

        Also, see the regular demands for ‘back doors’ in messaging apps and the implemented back doors (law enforcement access field) in things like cellphone ciphers, the Clipper chip plus the ‘helpful’ changes to certain encryption algorithms suggested by certain three letter agencies etc.

        1. The Spooks have always traded in privileged communications networks, and even more in secretly compromised communications networks..

          Read about Crypto AG for instance. Very enlightening. A peer-reviewed open source mathematical encryption scheme was distributed with an intentional backdoor. It lasted several decades before detection. There are definitely ones like it still undetected.

    3. Be grateful you’re not an inhabitant of the insect world – they dont have nuclear weapons but are ruthless x 10^6 compared to humanoids. Killing each other is very normal, even in their own families.

    4. If you think killing is the worst thing we do to each other, you have a lot to learn. I find it much more horrifying that we repeatedly structure things to perpetuate the disempowerment of victims of one thing or another, or punish them if they manage to empower themselves despite us. Pacifism is a virtue for the fortunate sheltered few; everyone else needs to be pragmatic.

  3. Thanks for the link to the article. I was a test engineer on both those computers at North American Autonetics Division in Anaheim, California. The shake test was essentially a huge speaker coil that screamed. We were told that each circuit board in the D37 cost as much as a Cadillac. All components were carefully tracked by QA.

    1. There are not “old nerds”, just nerds with so much of experience that they cannot find in memory in a suitable time what they are looking for.
      Not to mention that the engineer is the unsung hero of our times. Our eternal monument will be the ruins of this civilization.
      Chapeau aux nous!

      1. Then again;
        How do you tell an old nerd from a young nerd?

        If a young nerd breaks his eyeglasses, he fixes them with tape, and everybody laughs.
        If an old nerd breaks his eyeglasses, he fixes them with his microwelder and nobody notices.

    1. ISTR reading about it in a book on the U2 or the SR-71.

      Totally different (because they knew their altitude and that they were close to Earth) than the navi(astro?)gation used during Apollo, where they used the on-board sextant to get 3D angles on three(four?) stars and the AGC determined their position in space.

    2. Terrestrial sextant navigation is a great intro. Lots of great books there not to mention the ability to actually practice the theory. I’ve had a really hard time finding land based surveying techniques specifically finding altitude/elevation of things (like the elevation of a mountain top or something, not a sextant altitude. Confusing overlap of terms). Those methods use transit telescopes I believe. But if you just want to fix lat/long nautical techniques work well.
      As to celestial Astro-gation the sextants worked well enough on the Gemini and Apollo capsules (IIRC) but land based radar was a lot better for many reasons. One of the problems was the earth itself as a reference and actually getting a crisp horizon due to the atmosphere was hard. I can’t find a lot of literature.

  4. Sometime in the early 1960s, I bought one of those MM1 “disk drums” from a surplus place in Santa Barbara, CA. Figured to use it as the starting point for a computer. Gave that up after I took it apart and discovered what it really was.

  5. “we know nuclear weapons are frightening” do we? Are they? I am certainly not scared of them, and I don’t know anyone who is. Nuclear weapons are beautiful and awesome and a thing that has given us safety, all that clever science combined with destructive power and rockets. In fact, I’m not sure I can think of a thing that I like more Than nuclear weapons.

      1. The Minuteman militia, who themselves were “always ready,” or “at a minute’s notice.”
        The rockets, which were intended to be fueled and ready to go at all times, were named after the minutemen for the same reason the minutemen were so named. . .

  6. No one has mentioned the classic historical text on this topic, it’s a glaring ommission, technology is amazing, but it is always made by people:

    Donald Mackenzie (1993) Inventing Accuracy: a Historical Sociology of Nuclear Missle Guidance. The MIT Press.

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