Strike A Solder Joint Behind Enemy Lines

Imagine you’re out behind enemy lines in WW2, setting up demolition charges that may save the lives of your fellow soldiers. How do we make a solid connection between wires that will last? One of the solutions that were used by the OSS and SOE, the predecessors to the CIA and British Secret Service, were self soldering sleeves that could be lit like a match. [ElementalMaker] managed to get his hands on a box of these sleeves, and found that they work incredibly well, even after more than half a century.

The sleeves consist of a copper tube with solder and flux inside, and wax-covered pyrotechnic compound around the outside. A small blob of striker compound similar to a match head is used to set the soldering process in motion, using the striker surface on the outside of the oversize matchbox that the sleeves are packed in. The pack that the [ElementalMaker] got was made in 1964, but is supposedly no different from those used in WW2.

When lit, the pyrotechnic compound does not create any flame, it only smolders, probably to make it safer to use, and avoid detection at night. As the solder inside the sleeve melts, the operator is supposed to push the wires further into the tube to make them overlap. Although [ElementalMaker] didn’t cut open the sleeves, it definitely looks like a good joint, with solder oozing from the ends. Check out the video after the break! If you want to get your hands on a pack of these sleeves, it looks like a military surplus store in the UK managed to source some.

As horrible as war is, it’s undeniable that it inspires some creative innovations. Like soldiers hacking together parts from multiple guns to serve their immediate needs, or making guns shoot through spinning propellers without damaging them.

43 thoughts on “Strike A Solder Joint Behind Enemy Lines

  1. A pyrotechnic compound which burns without flames have another advantage in this case: Flames (hot gases) would carry the energy away, a glowing solid concentrates the energy on the metal tube.

  2. I’ve used these back in the Sixties. We had a Combined Cadet Force at school, and used to use the old style field telephones at sports days and other events. These were handy for connecting the steel/copper telephone wires; they were wrapped with insulating tape after the joints had cooled down. You had to be cautious when pushing the wires in, since solder tended to spurt out of the ends of the tube… :o

    1. “You had to be cautious when pushing the wires in, since solder tended to spurt out of the ends of the tube… :o:”

      A real man wouldn’t complain about that! (I probably would have cried like a little girl through.)

    2. Snap, I was at a scottish military boarding school in the 60s, and our CCF unit was signals based, we used to use these for joining cables when running field telephone lines. The cables used for that where a pain to join any other way as they where multistranded steel cores (for durability), so you could not twist them together etc.

    1. Those are commonly used in automotive applications where it’s a PITA to get a good crimp splice on and crimp it.
      A small pencil torch can be stuffed into tight places more easily, and aluminum foil is a great temporary heatshield for keeping heat away from things not needing heating.

    2. That looks like great suff. Those small colored lines, do they form a watertight seal?

      What I actually do miss in that video, is a conductivity test. First run enough amps through the wire to see at what amp it starts to melt and burn. Then make one of these connections, and check how many amps it can take before the connection breaks or burns or whatever.

      1. The good ones form a solid joint and do seal.
        The cheap ones are iffy on both their connection and sealing capabilities.

        I have a few boxes of Ratheon branded ones, and when I use them, I typically slide the solder splice up one wire and twist the wires together, before sliding the splice back over the joint.
        A touch of flux or pre-tinning the leads doesn’t hurt either, if they are anything but clean wires.

      2. “Those small colored lines, do they form a watertight seal?”

        To me, those colors seem to be a common way to indicate what wire guage the connector is designed for.
        It would be nice if they are watertight, but that may not be what is implied.

        1. They do seal the wire while serving as a quick way to see what gauge they are. Used them a lot on EDMs when I couldn’t get an iron in somewhere, they’re definitely watertight.

    1. In the UK you have to post pyrotechnic material using specialized carriers who have the appropriate safety protocols (i.e hazard warning labels and knowledge of WTF is actually on fire in the lorry)

      Royal mail publishes restrictions for things your allowed to post –—advice-for-personal-customers

      USPS also publishes restricted items –

    2. Well there’s “pyrotechnics” and “PYROTECHNICS”…these little would qualify as the lowercase version.

      In addition to USPS (United States Postal Service, i.e. the government) there are also private carriers like UPS and FedEx. I know for a fact they will ship reasonable quantities of almost any “HAZMAT” as long as it’s declared…ammo, gunpowder, fireworks, flammable liquids, whatever else you can imagine.

      I doubt they would even put these self-soldering splices on a HAZMAT truck, just a brown box as far as they’re concerned…no more dangerous than the 1000lbs of cardboard in the trailer.

        1. I think it’s anything “D” or smaller is considered safe as-is…I used to order re-loadable motor parts in the F and G ranges, but they had to be shipped as multiple “grains” for safety.

    1. theres such a thing as bad instructions. the second you strike the thing, you suddenly have given yourself a time limit to read and execute the next item on the list. which is hard if you are watching the pretty fire while making a youtube video.

      the good news is anyone who actually had to use these things in the field probably got some training in their usage before hand.

  3. I recently found out about a material that behaves like this, if one wanted to DIY, but I don’t yet have a name: some small foundries pour a bunch of it on top of a just-completed casting and it burns similarly to this to keep the aluminum at the top of the riser hot so it can more effectively fill in the mold as the main body of the mold cools and contracts.

  4. During WWII my uncle was in the US signal corps stationed in China. He said he built a AM receiver out of salvage parts (receivers weren’t allowed in camp) with a speaker cone made of paper and a coil from a firing solenoid salvaged from a remotely operated machine gun. He said the camp power varied from 220v in the daytime to 120v at night, when all the lights were on, so he built a tapped transformer to power his rig. When the camp commander saw it he let him keep it, saying “I don’t know what that is”.

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