Britain’s Experimental Viper No.3 SMG/PDW

A series of very compact submachine guns – possibly better described as personal defense weapons – was made in Britain at the end of World War Two under the name Viper (as an interesting aside, snake names were popular – the EM-1 and EM-2 were code-named Cobra and Mamba during the same timeframe). The first was a simplified take on the Sten, but the No.3 Viper here is a wholly new gun made from the ground up. Designed to hang under the arm and be used either with or without the detachable shoulder stock, it is chambered for standard 9x19mm ammunition. Oddly, the No.3 Viper uses MP40 magazines, instead of what should have been ubiquitous Sten magazines.

According to Matthew Moss at The Armourer’s Bench, the project was organized by a Mr. Oliphant of the Ministry of Supply, and the design team included Derek Hutton-Williams (later to be superintendent of the Royal Small Arms Factory, Enfield and the director general of Britain’s Royal Ordnance Factories) and Messrs. J. Soutcott and W. T. Walker.

Many thanks to the Royal Armouries for allowing me to film this tremendously rare artifact! The NFC collection there – perhaps the best military small arms collection in Western Europe – is available by appointment to researchers, and anyone can browse the various Armouries collections online.


  1. This little chopper is so off the wall that you have to love it.

    At a time when Britain was knee deep in Stens, it does seem a little niche to develop an SMG for MPs in Germany, but there you go. Perhaps the reason MP40 mags were used was precisely because it was for use in Germany, where these would I assume have been ten a penny back then.

    It would have made a splendid resistance weapon if it had been made during the war. It would have been ideal for the hit on Heydrich for a start. It would have been very useful for a resistant to have been able to sling a discreet SMG under the raincoat whilst travelling, ready to give any nosy Gestapo type a nasty surprise.

    I must confess I had thought that Sten mags were interchangeable with MP40 mags, but one SMG which I think did use MP40 mags was the Atchisson M1957, which was also a mini SMG, which seems to use the magazine housing of an MP40 as its basis. Full marks to Ian if he can produce a video on that one.

    • The reason for using MP40 mags was because the weapon was intended for use by Military Policemen in occupied West Germany after the war. There were plenty of surplus MP40 mags floating around! The idea was that MPs could hipfire this thing one-handed while sat on a motorcycle. Idea didn’t get very far though.

      I wrote a piece about it here:

    • “If you’ve got nothing good to say to anyone, don’t say anything at all.”

      That’s what Mom said to me. After all, throwing flak at people just to be mean to them doesn’t earn me any coin.

  2. I’m guessing that by 1945, British armorers had heard about eight zillion complaints about crappy, unreliable, fragile Sten-gun magazines. And if there were an equal number of complaints about MP-40 magazines, most of those weren’t made in earshot of British armorers or even in English. Since there was at that point no shortage of MP-40 magazines for anyone who wanted them, the grass is always greener etc.

  3. I’ve always wondered why they didn’t do something like this (simply put the grip on the mag well of a Gen 2 SMG, and a buttplate on the back, for a compact gun with a real cheek weld instead of a spindly folding stock). This video shows how warped execution probably turned people off the idea.

    When designing a compact arm (SMG, etc.) the discussion should be whether to use the ergonomically optimum length of pull (generally regarded as 13.5″, although Karl – who isn’t small – says most people given adjustable stocks will gravitate towards the 12.75″ of the M-16A1), or trade off a little ergonomics for something more compact.

    Every time I see a “short” weapon with a grossly extended buttstock like this, I just want to scream “WHYYY?!”

    • Hey Mike, should wee show them “cranker”? I think Ian would publish it. Man, there would be a race stateside, who can do it better 🙂 My ‘author right’? I don’t give it hoot.

        • Hey Mike, is that a compliment or what? 🙂

          Tell ya what – every pseudo-artist, no matter what trade they are in, instinctively feels an urge to “patent” a contraption they dreamed out. I have the opposite idea – throw a piece of meat among the dogs and let’s see what will happen!

          Let them fight and then collect the profit! 🙂

  4. Commenters on the Viper Mk I video mentioned the idea that the Viper was intended for motorcyclists (“shoot twenty rounds and get out”). The possibility of shooting at fleeing crowds (of criminals?) gets mentioned both here and there. Does nobody remember the “defense” part of PDW? Patrolling an occupied enemy state, you face the possibility of a mob rushing towards you. I think that’s the answer to the question, “What were they thinking?” — but mind you, I don’t assert they were thinking all that clearly.

    • PS. I reviewed the Viper Mk I comments on YouTube. Comments for the Mk I on this site do mention defense against mobs. Also that the Mk I prototype dated from 1942, so perhaps could have been intended for Resistance movements.

  5. Considering the ubiquitous plethora of STEN guns after WW2 no wonder this Viper SMG went nowhere.

    The layout of the Viper SMG reminds me of the later Uzi and similar sub-machine guns with the magazine in the grip.

    • ” … wonder this Viper SMG went nowhere.”
      They collected the poison and let it out to wild. Never heard of after 🙂

    • Ah the curse of virtually all post-war small arms “Why spend our limited money on a slightly better product when we captured more German ones than we know what to do with?”

  6. Dear Ian,
    Thanks for showing us another obscure and oddly configured SMG.
    How long is the Viper Mark III’s “pull”, measured in inches from the buttstock to the trigger?

    On a related note, what do you think of the USAF’s recent announcement that they plan to install dis-mantled “shorty” AR-15s in ejection seat survival kits?
    What do you think of a downed pilot needing to pin together the 2 different pieces while running from bad guys?

    Finally – in your opinion – what is the ideal Personal Defense Weapon for a military pilot shot down near Taliban Town?

    • “… what is the ideal Personal Defense Weapon for a military pilot shot down near Taliban Town?”
      I doubt Ian has time/ capacity to respond. You want to talk of Taliban? You would be well advised to clear that bunch as far as you can. They ran A-n before invasion rather efficiently and with iron fist. No one dared to cultivate poppies.

      But to your question. My pick would be 7.62x25mm Tokarev. Good range, good penetration, simple and foolproof. They have also plenty of vintage ammo to stuff into it.

      • I heard from ethnic Chinese person that the Chi-com pilots were carrying Tokarev pistols with one full magazine. No spare required. If you think about it makes sense. When you shoot, make sure you hit. One shot-one man down… and then you run, as fast as you can.

  7. This is definitely something of a “spy weapon”.
    Designed to be used with one hand from under a raincoat or coat.
    As compact as possible, especially flat.
    Designed to use enemy ammunition and magazines.
    Adapted for the installation of a suppressor.

    The purpose of drilling in a barrel is the same as for Agram.
    Reduced bullet speed and bolt weight.

    • Good observations Stiven,
      I would only add that to shoot from under the coat you need different ejection that to side. How was in on Spectre SMG?

  8. Re MP40 Magazine.
    Perhaps the designer/s (of Viper No.3) were aware of STEN Magazine malfunctions id est cartridges jamming in the double to single column transition zone.

    It would seem the MP40 Magazine were made or modified by the addition of corrugations to limit friction on cartridges in order to prevent cartridge column jamming.

    The Schmeisser Myth: ref p275-295 in particular p278

  9. I recall when Hinckley shot Reagan, undercoat burpguns appeared like magic.
    As for landing in Taliban Town (after they just got over their airstrike?)
    Where can I get one of those ‘Predator’ atomic wristwatches?

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