In Special Forces from 1960 to the mid-1980s, there was a capability called, among other things, “the Magic Rucksack.” (This weapon, and its mission, were prolific producers of slang and nicknames, most of which were as compartmented as the mission itself; it’s unlikely anyone knows them all). It was the Special Atomic Demolition Munition, SADM, a small nuclear fission weapon with a W54 selectable-yield warhead, detonated by timers. It was the smallest of a series of ADMs that specialist Army engineer units trained with.

This is the Medium ADM, “field-stripped.” Components of the SADM were similar, but smaller.

It fit a very, very narrow target niche. While the engineers’ wartime mission was to use their ADMs to channelize advancing forces into artillery and air “kill boxes” (any Ivans they actually nuked were not the main objective, but what a fisherman might call “bycatch”), to justify an SF SADM emplacement the target had to meet certain criteria. If you think about it, you can probably come close to what they actually were.

  1. Payoff. It had to justify being targeted with a <1-1kt nuke;
  2. Deep. Deeper behind enemy lines than artillery could reach; and,
  3. Not a good target for an air raid.
  4. Target placement achievable by SF ODA.

There were two ways to carry it, in its own container, which felt like it was designed by some pointy-headed nuclear physicist who’d never carried anything on his back in his life, or wrapped in a sleeping bag or poncho liner inside an ALICE or mountain rucksack (depending on period).  There was also a transit case for administrative transit; there’s no scale in this picture, but it was too bulky for field use by far.

Transit Case.

This video is sometimes presented as SEALs or Marines, but it was a joint Army/Navy exercise. The men preparing the SADM for aerial delivery are wearing 1950s-60s Army uniforms and were probably engineer officers and NCOs from Sandia Labs.

(I can’t find the specific video anymore. The link was dead)

SADM

As you might imagine, security around the weapon was heavy with even its existence being classified. Teams selected for SADM duty were given additional security clearances and briefings, and underwent considerable classroom training, including usage and employment information as well as hands on assembly/disassembly of mock-ups and simulators. There was never a full-mission-profile test with an actual warhead. Indeed, most SADM team members never saw an actual SADM, only simulators.

The M46 simulator matched the weight, bulk, awkwardness and shape of the actual weapon, and contained timers that worked about like the ones in the real weapon, except for the world-shattering Kaboom! at the end.

kaboom

Even the simulator was a classified device. A classified manual described the usage, effects, tactical employment, and technical features of the weapon, and provided real timer drills; a companion, unclassified manual provided practice with the math and timers of a slightly different, notional ADM.

The security was breached by CBS News in the 1980s, and they aired a short film clip of a 1st Battalion, 10th Special Forces Group SADM team in training in 1986. By that time, though, the writing was on the wall for the Magic Rucksack.

The SADM was probably a more fitting component of the battlefield mix in 1960 than it was by 1985. Precision-guided munitions such as cruise missiles were capable of hitting a lot of targets more exactly, and with less risk of interception, than a team of men crunching through the woods.

Moreover, by the mid-1980s, environmental problems had forced the shutdown of several  US nuclear-weapons facilities, some temporarily, some permanently. With scarcity arriving the same time that tactical and strategic nuclear modernization called for new warheads, the recycling of the fissionable material from the SADM’s W54 warheads was inevitable.

There are constant rumors that the SADMs were stored. That might actually be the case with some components of them, but it’s more likely the components were destroyed. (The same fate befell the engineers’ three sizes of ADMs). The fissionable material, the heart of any nuclear weapon, was needed elsewhere, and that more than anything wrote finis to the 25-plus-year saga of the Special Atomic Demolition Munition.This entry was posted in SF History and LoreThe Past is Another CountryUnconventional Weapons on  by Hognose.

Post Script

As the comments section was always surprisingly worthwhile I will include them here as well. I did my best to maintain the formatting.

24 thoughts on “The Magic Rucksack”

  1. looserounds.com

    seems I recall John Plaster mentioning in one of his books on SOG that each Special Forces Group had a team of guys just for inserting these things? I believe he informally called it a “suitcase nuke” . If memory serves he also mentioned that some of the early HALO guys were the ones with the mission of inserting this contraption? or is my memory all over the place ?I have always wondered how the fellows were supposed to get away from the thing before it went kablooey
    after they set it up, was it just routines special forces escape and evade or sneak out kinda stuff?now that yo uhave my mind starting to do the one thing I try to avoid in the middle of a work day. I got to go look up and read about that small artillery piece that fired the small nuke artillery warheads . gonna search your fine website and see if you no doubt already have written on it in the past. I see a never ending trail of links in my immediate future
    1. Hognose Post author

      You were to set the yield, set the timers, walk away and put a couple of terrain features between you and the kB, and bury your radios, then at T-x minutes (the timers were built in the 50s and 60s and nobody would vouch for them having quartz accuracy) you were to lay down, feet towards blast, head away, eyes shut and mouth open until the blast wave had passed.Bear in mind, this was a little nuke, not a city-buster. It gave an SF team a way to take out a structure too robust to be destroyed by a man-packable quantity of HE.
      1. Kirk

        I don’t know about the SF missions, but the 12E Atomic Demolition Munitions specialists that made up the (I shit you not about the unit title, here) Disposable Fire Teams were required to maintain eyes-on coverage on the munition until it detonated.Precisely how that was to work, and ensure survivability of the team, I have no idea. Overwatch with filtered binoculars, which were not on issue in the units? Dedicated Kamikaze American troops? I don’t think so… The rules weren’t going to be followed, as best as my 12 E compadres related to me. They were told to do “A”, but the reality was that it was probably going to be Course of Action “B”–Put it in place, and run like hell.Couple of things came out of that program, supposedly–One was the Alice Large ruck, which was reputedly developed for the SF Blue Light teams to be able to carry the SADM, and became general issue once everyone else saw the damn things. There was also a bunch of specially developed comms security devices that were supposedly put on general issue after it was realized that it was even possible to miniaturize the gear for doing the permissive action links with the SF teams. We supposedly had general-issue COMSEC items specifically because of that program, for what that was worth. I’ve never seen anything in print, confirming that, but my old-school commo rats all insisted that was the case.The other point about these things is this: As you allude to, the idea was to use these things to channelize the enemy forces into convenient kill zones. The real reason we had to do that, however, goes to the issues with doing really large demolition projects, in terms of time and materials. If you go back to the WWII era, and look at the problems the Germans had with defending the Rhine, you’ll remember the so-called “Bridge at Remagen”. At that location, despite months of careful preparation, the demolition failed, and the Allies jumped the Rhine using that bridge. The German engineer officers who were responsible wound up executed by the Nazis.But, the basic problem remains that demolishing large bridges and other targets like them is neither easy nor logistically trivial. The movies show such things as being easily demolished by man-carried explosives, but the fact of the matter is that no amount of finesse can take what even a large team of troops can carry and turn it into a successful demolition job. I loved the “Force 10 from Navarone” movie, but… Jeez. That sucker is just about as technically possible as putting your head between your legs and farting to the moon, using conventional explosives. Sergeant Miller could have pulled that job off with a SADM, and that’s about it. You want an instantaneous demo job pulled on a large structure, without weeks of preparation and a trainload of conventional explosives, you’re talking something that’s exclusively in the realm of pocket nukes. The same goes for all other large structures like tunnel complexes, dams, and other items. The Golden Gate bridge is just not going down to a couple of guys with a truck bomb, I’m afraid–Not in any meaningful sense, that is. At Remagen, the demolition went off, but did not completely destroy the target. As such, it was repairable, and enabled the US forces to put a bridgehead across the river long enough to establish a pontoon float bridge that really did the lion’s share of the work.
        1. looserounds.com

          wow interesting commentI didnt know that about the large ALICE
          Hognose. did you ever get issued or test some gear issued to you that later went on to be issued to the rest of the Army? other than the SOPMOD kit of course
          1. Hognose Post author

            Yeah, like gore-tex outerwear which became the ECWCS (Extended Cold Weather Clothing System). sleeping pads instead of air mattresses (we were buying foam pads at REI or EMS). We also tested a lot of stuff that uncle wound up NOT buying, sometimes for other reasons (for instance, chocolate brown boots that were gore-tex jungle boots — they were fantastic, but the soles wore rapidly on pavement). And sometimes cause they sucked (Trebark camouflage). We also had a guy rig up a forerunner of a Camelbak at least ten years before that hit the market.
          2. ODA564

            The SADM barely fit in the large ALCE.
  2. Gray

    Payback, by J. C. PollockRead it circa 89. Fun at the time.
  3. oberndorfer

    http://www.geschichtsspuren.de/artikel/34-verkehr/135-sperren-wallmeister.html
  1. Kirk

    Huh. I think I have a comment hanging somewhere in the system, and I’ll be damned if I know why…
    1. Hognose Post author

      I dunno. Perhaps Akismet tagged it due to length. It has been sprung from the spam jail now.
  2. Tim, ’80s Mech Guy

    Remember seeing that on the news, kinda hope the concept did not die completely on our end, some goat-rapist in Darra is trying to reverse engineer that from wikipedia as we speak…Davy Crocket, now that’s a GUN!
    1. Hognose Post author

      Same basic warhead as the SADM, the W-54.
  3. S

    Thanks Mr Oberndorf for that excellent link. I’ve noticed quite a few of the storage sites for the demolitions gear scattered about, and thought the remote ones were for pre-surveyed artillery positions; maybe some were. Couple that with the bullet hole in the local church’s window from the 30 years’ war, the dead froggy General in the boneyard, and the gun pits on the ridge opposite from 1871, and I get the impression things get sporty hereabouts on a generational basis. It’s been uncharacteristically quiet of late….
  4. Tim, ’80s Mech Guy

    My German sucks, but those prefab obstacles remind me of the ones in the northern ROK. Basically a concrete pass through a mountain saddle or one of the cross country walls with concrete blocks-sometimes one big block sometimes a bunch of smaller blocks-set to come crashing down upon detonation of a series of small charges. Some of the ones north of the river looked wired already but they looked un-maintained circa ’86.
    1. Kirk

      The Germans were several orders of magnitude more sophisticated than the Koreans, although the Koreans were a hell of a lot more diligent about actually doing the rest of the necessaries to go along with it all. If you were to drive south from the DMZ, there were about five completely separate defense lines, all with pre-prepared obstacle belts, fighting positions, range cards (in brass or painted on the concrete of the bunkers) and a whole host of other preparations. The ROK Army was also prepared to fight from its camps, which we never bothered with, nor did the Germans. Had the North Koreans ever come south with total surprise, odds are that they’d have caught us with our shorts around our ankles, and the ROKA guys would have been like “Oh, an attack on our base camps… Must be Tuesday, or something…”.Biggest problem I saw with the German preparations was that they were mostly half-hearted. They never truly wanted to believe that their homeland might become a battlefield, so they balked at all kinds of common-sense ideas, like moving the woodlines and so forth along the Inner German Border to enable better fields of fire for the ATGM assets, or to put all the electrical transmission lines underground so as to not have the interference from their lines screw with the wire-guided missiles. If the Germans had been willing, we’d have had successive lines of prepared defenses, just like Korea, but they were just not up for it, and it proved to be the right choice, in the long run. Had they ever had to fight WWIII on German territory, however? We’d be discussing the ramifications of their refusal to properly prepare, and how many NATO lives it cost.At this point, in Korea, the biggest problem for the NORKs is going to be South Korean traffic. We used to joke, back in the 1990s, that if they’d ever have invaded, like as not we were going to be heading north on the northbound side of the highways, and we’d pass each other, stuck in traffic, with them heading south. We’d have to pull off into rest areas to actually be able to engage each other… And, if you’ve ever tried moving in Korean traffic around a major holiday, you’d probably agree with me. The other thing we used to joke about, only somewhat facetiously, was that the North Koreans would come south, hit the South Korean traffic and spend about a day dealing with the various hazards thereof, like the well-known Terminator dump trucks, and they’d turn around and head north, scared out of their wits. South Korean traffic is that bad–I’m pretty sure that they recruited the cab drivers from among the ranks of former Japanese Kamikaze pilots. God knows that if they didn’t, they were missing a bet. You’ve no doubt heard of the Crazy Ivan? Well, trust me on this–The Russians have nothing, absolutely nothing on the South Koreans when it comes to sheer insanity on the roads.
      1. Tim, ’80s Mech Guy

        Traded mirrors with a dumptruck on MSR 3 one night, glass everywhere and we did not get a scratch. I drove from Casey to Yongsan about twice a week usually in a TMP sedan or a humvee but that night a SATCOM five ton needed to go south to some mystery destination only the E-6 knew about-that shit was pretty high speed back then and they issued ammo before we left, only time I got ammo for a trip south. Two hour trip turned into six and it was the only time I got caught in a real traffic jam. Stuck in traffic about dark dipshit finally decides to break out the map and show me where we are supposed to be. We were sitting in sight of the Blue House and our destination was CP Soeul. I go there twice a week.
        Taxis and Kiamasters were most of the traffic in those days and the motorcycles/bicycles of course. Those were the days when you’d see antiques all over the place, ROK M-47 tanks and the occasional 3.5 Bazooka, Garands and Carbines were in abundance with reserve or rear eschelon troops I guess. The guys up north had 16a1s and The K1A1 was coming on line. If your shit got ripped off in the field you had an idea wether it was roks or the sliky boy, roks would steal 30 rounders but sliky did not want to get cought with them. I always thought that was kinda suspect though getting caught with a bag of pro masks was gonna get you screwed anyway…
        1. Kirk

          Oh, yeah… Slicky boy. That sumbitch was smart, fast, and likely tied into the entire intel apparatus of the South and North. Nice thing was, by about 2000 or so, he was pretty much more interested in playing Starcraft down at the local computer bang shack than he was in ripping us off–That was too much damn work. Kinda the same way you couldn’t find an actual Korean bar girl past about 1995, either. In 2000, all that shit was subcontracted out to Russian expats and Filipinas…The thing I never could quite get over, though, was Ajima. That woman would be out waiting for us at the local dispersal area, set up before we even got the alert. And, she’d have hot ramen with “cheesy egg hamburg” waiting for us, along with Yaki Man Do, and that weird-ass Korean pre-sugared and creamed instant coffee. Used to drive our commander absolutely nuts, that did. He finally just gave up, and went with it, working through our KATUSA Sergeant Major. She was better for morale with that damn Ramyun and “coppee” than about anything else–And, oddly enough, when she was in the perimeter, slicky boy stayed the hell out.We heard one hell of a racket, one night, and went out looking with NVGs. Ajima and her two sons had some local idjit caught up just outside our perimeter, and she and her sons were beating the holy hell out of the poor kid, and I don’t mean that lightly. One son had a pick-mattock handle, and the other one was using a baseball bat, while Ajima was screaming out the riot act at the kid. Apparently, according to my senior KATUSA, she had the concession on us, and the only people who were going to be ripping us off were going to be her family… And, all she wanted was a good price for her Ramyun and Yaki Man Do. Scary little old lady–You absolutely did not want to miss paying your tab with her. We had one idiot refuse to pay her at the end of an exercise, and he spent the next month or so afterwards running into her or her sons down in the ville, and they were always where he wasn’t expecting them, either. I kept telling him to pay up, but he wasn’t one of mine, and his boss didn’t care. Well, until he got run over by a bus, that is… He promptly paid up after he got out of the hospital, with interest and a large honorarium. He was pretty sure he wasn’t pushed, but he found it just felt safer to pay up the fifty or so bucks he owed.Korea was a damn trip, about that time frame. We still had houseboys in some of the buildings, and those guys made bank. The one in my company barracks would come into work looking like the poster child for poverty, leave looking worse–And, then go outside the gate, clean himself up above one of the bars he owned downtown, and go home in a top-of-the-line Ssangyong SUV that was a better car than the mayor of the local city drove. His kids were all professionals, either doctors, lawyers, or dentists. Whose college he’d paid cash for, btw…
          1. Tim, ’80s Mech Guy

            I knew it had gone down hill but subbing out the whores? Day-um.Only time slicky got us bad was one night when we were supposed to jump-pull up the TOC and move- at about 0400. Something went wrong with the Jump Tac, we ran two theoretically identical circuses, one was always supposed to be up and the other in transit, and nobody passed the word. Ajima packed up and split after midnight, like you say she knew where we were going. After guard I hit the rack for what I expected to be three hours of sleep and woke to sunshine and my boss saying to check sensitive items. Pro mask gone, camera gone-it was in a mask carrier-and nobody heard a thing. The thirty rounders were still there so the roks got a pass, they had a twin fifty permanently emplaced down the ridge a bit looking over a valley that had to be five miles or more across so the guns were next to useless but they had a awesome view.
  5. Jim Scrummy

    Love Marvin the Martian! I’ve trained my kids to speak like him with the “XQ39 Space Modulator” voice.
  6. Ben

    Good FP article on this from awhile back. Great pictures and animations. Also liked the name:
    http://foreignpolicy.com/2014/01/30/the-littlest-boy/
  7. Raoul Duke

    Great stuff!I’m curious, though…what was the all-up weight of this contraption, ready-to-fire?
    1. Hognose Post author

      It was heavy — maybe 90 lbs. Pu-239 is extremely dense stuff, and the weight was driven by the “physics package”. The shielded canister and jump/carry rig were only about 30 lb without the simulator inside.
  8. ODA564

    The article contains one mis-statement.A W-54 with the pit removed was deployed and detonated during a Nuclear Surety Inspection (NSI) by an SF “GREEN LIGHT” ODA. To my knowledge (and from the Sandia Labs observers statements) this was the only time it happened – details redacted but available.In 5th SFG(A), it was the ‘magic mission’. After a Group commander was relieved for a minor infraction of the Personnel Reliability Program (PRP), having an upcoming NSI was a ‘get out of Support Cycle free pass’.The SADM or GREEN LIGHT company (ODB 540 or A/2/5) consisted of 2 combat dive ODAs (542 and 564, IIRC) and two MFF ODAs (544 and 564) – the 56_ teams were in ODB 560 (C/2/5) on the UMR (unit manning report) and then attached to ODB 540 (I think our rucksack teams were attached to ODB 560 since their focus was mountain warfare – ODB 550 was, of course, in those days “Jim Guest’s Pets” at Mott Lake and ran SOT).I know… the kids are saying “What’s Support Cycle?”And no one has mentioned how the Engineer School (at Belvoir!) destroyed the VHS tape we (ODB 540) sent them of the artful ballet that was a 5th SFG(A) receipt inspection? They were afraid the Engineer MADM and SADM units would copy it!Think I was honor graduate of the SADM Employment Course. Too bad I couldn’t get that on my ORB or DD214.
    1. Hognose Post author

      I did not know that anyone had ever tested a SADM (minus physics package). It does make sense that they would do that occasionally. Otherwise, how do you know it works?In 10th we called it “red cycle” (the cycles on the post training calendar were color coded r/y/g). It seemed like it ran longer than green cycle, and ate most of yellow cycle too, when we were supposed to be doing courses.I have pictures of eee-light Green Berets, in their green berets, swinging swing rakes and driving lawnmowers.LMAO about you trying to get the SADM course on your ORB.

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