STEN Magazine Loaders

While the ongoing Coronavirus pandemic has prevented some archival research I had planned which would have informed much of the STEN series, our good friend Richard at the Vickers Machine Gun Collection and Research Association, has come to our aid and we’re able to cover some of the loading accessories developed for the Sten’s magazines.

As we know the Sten uses a 32-round double stack, single feed magazine which can trace its origins back through the Lanchester Machine Carbine to the Haenel MP28,II’s magazine designed by Hugo Schmeisser [patented in 1931].

Sten Magazine, inert 9x19mm rounds and MkII and MkIV magazine fillers

The nature of the single feed makes the magazine difficult to load by hand with the last few rounds very hard to insert. So a series of four marks of ‘magazine fillers’ were developed. These are described in the British Army’s official List of Changes in February 1943.

The MkI is described as consisting of “a lever mounted on a short case which conforms to the shape of the magazine. It is hand operated, the loading lever being given a rocking motion during filling. The MKI slipped over the top of a magazine with a rivetted spring tab which indexed into a notch in the front of the Sten mag.

A cutaway showing the MkII filler

The MkII is very similar but simplified by having the spring catch mounted on the rear instead of the side and engaged a “small rectangular slot on the magazine”. The rear of the spring is turned up slightly to allow the user to remove its from the magazine.

The MkIII, which is possibly the rarest of the fillers, is described as:

“hand operated but of different design from the MkI and MkII. It consists essentially of a spring loaded vertical plunger which is attached externally to a case, the latter to assemble on the magazine. There is no retaining catch. It comprises the following parts:

Case. Is a rectangular shaped steel pressing with a tube of rectangular section welded thereto. The latter, which houses the plunger and spring, has a hole trilled at the lower end to accommodate a pin which restricts the amount of movement of the plunger and acts as a stop for the compressing spring.

Plunger, loading. Is made of two laminated steel strips welded together the top part of which is set to form a handle. The body of the plunger is slotted to accommodate the compression spring. The top part is splayed to form a suitable contact with the cartridge.”

List of Changes, Feb. 1943
Sten accessories including a sling and a MkII magazine filler

The other more common filler is the MkIV. Which is a much simpler design with a loading lever mounted on top of a clip which is attached to the rear of the magazine body and retained by a spring similar to that of the MkII.

Rich has very kindly demonstrated the use of the two most common fillers – the MkII and the simpler MkIV. It takes Rich just under 2 minutes to load that magazine, but he was doing his best to show various angles and unlike a British soldier during the war he hasn’t regularly loaded magazines with one of these fillers either. Despite that the clip gives a good idea of how fast you could load a mag once you’re in the groove.

With the MkIV filler Rich was able to load the mag in about 1 minute 15 seconds, the stability of resting the base of the mag on the table helped with the MkIV’s simpler design.

Manual diagram showing both the MkII and MkVI

Also, as a follow on to our previous episode looking at the Sterling Submachine Gun’s magazine Rich has also demonstrated the loading of a Sterling mag to its 34 round capacity. No magazine filler needed with George Patchett’s double-stack, double feed magazine.

Massive thanks to Richard for taking the time to film the clips used in the video. please do go and check out Richard’s channel and www.vickersmg.org.uk.


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The M8 Greyhound Armoured Car

During the Second World War the US Army sought a light, nimble tank destroyer. The M8 developed by Ford ticked the Army’s boxes but by the time it entered production it’s 37mm gun couldn’t penetrate thicker enemy armour. Instead the M8 was pressed into service as a scout car.

An M8 during testing at Ford (US National Archives)

The M8 first saw action in Sicily in 1943 and subsequently saw service in every theatre of World War Two. One M8 reputedly knocked out a German Tiger II during the Battle of St. Vith, in December 1944.

The M8, while excellent on roads, did not perform well across country because of higher ground pressure from its wheels and its suspension system. Largely confined to roads when terrain or conditions were bad the M8’s thin armour also proved vulnerable to enemy mines. This was a problem first encountered in Italy and later in northwest Europe.

A 79th Infantry Division M8 Greyhound destroyed by mine near La Haye Du Puits, France (US Army)

Despite its shortcomings the M8 remained in service long after the war and many were sold as surplus with them continuing to be used throughout the Cold War all over the world. Some 8,500 were built.

Sources:

Tank Demonstration – Ford, US National Archives (1942)

M8 Greyhound Light Armored Car 1941–91, S.J. Zaloga (2012)


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Bring Up The PIAT! – A Bridge Too Far Scene Analysis

A Bridge Too Far (1977) is undoubtedly a classic of the war film genre, massively ambitious it attempts to tell the story of Operation Market Garden. One of the key stories told is that of 2 PARA besieged in Arnhem awaiting relief from XXX Corps.

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A PIAT waits for the ‘Panther’)

Perhaps one of the most enduring scenes sees Anthony Hopkins, portraying 2 PARA’s commanding officer Johnny Frost, spot an enemy tank approaching and bark the order: “Bring Up The PIAT!”

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Set photo from A Bridge Too Far (Airborne Assault – PARA Museum)

If you follow me over on twitter you’ll know that I use this famous line as a hashtag (#BringUpThePIAT) whenever I discus the Projector, Infantry, Anti-Tank. I thought it would be fun to break down the iconic scene and see just how accurate it is.

The scene itself is actually quite authentic. The PIAT gunner misses, and that isn’t too surprising as despite being a platoon weapon not everyone had a lot of training on them. While the PIAT misses twice – this is because the gunner was firing from an elevated position. This makes judging the range and lead which should be given to an advancing tank all the more difficult. It is something we see in contemporary accounts, including in Arnhem Lift: Diary of a Glider Pilot, by Louis Hagen. Hagen describes firing a PIAT at a self-propelled gun (likely a StuG) from an attic during the fighting in Arnhem: “The direction was perfect, but it fell about twenty yards short.” Similarly, there are accounts from Home Army members fighting in Warsaw during the Uprising which describe exactly the same thing.

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The second PIAT shot in A Bridge Too Far

While the flash we see in the scene might be excessive the recoil is quite authentic. While writing my book on the PIAT, I did a lot of research into the cultural impact of the PIAT and the numerous films it appeared in since World War Two. I recently wrote an article about the numerous films it has appeared in, you can read that here.

Perhaps the most important and realistic appearance was its first, in the fascinating 1946 film ‘Theirs Is The Glory‘. It’s a unique film that was filmed entirely on location with from veterans of the battle making up most of the cast and help from the British Army’s Army Film and Photographic Unit.

The PIAT appears twice in the film, scene some PARAs are trying to fight through to Arnhem but have been pinned down by what appears to be a French Char B. As a sidenote captured Char B1’s in German service were present in Arnhem).

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‘Theirs Is The Glory’ Film Poster (Airborne Assault – PARA Museum)

The PIAT team are seen to move to the flank to get a good shot at Char B. The short scene gives a good indication of how the No.2 would load the PIAT as well as showing the rate of fire possible – a good team could get off five rounds a minute. Theirs Is the Glory also features another brilliant PIAT scene with Corporal Dixon seen knocking out a Panther

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PIAT Team in action in ‘Theirs Is The Glory’

I would highly recommend both films as they are both interesting depictions of the battle and both good representations of the PIAT in action.


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We Have Ways of Making You Talk Discuss ‘The PIAT’

Al Murray and James Holland discussed my new book about the PIAT on a livestream for their great podcast ‘We Have Ways‘, please do check them out – here.

Massive thanks to Al and James for their enthusiasm about the book (and the PIAT!) and for their kind words about it! Al gives a nice short rundown of some of the areas I cover in the book. [You can watch the entire livestream here]

The book explores the design, development and operational history of the PIAT. If you’d like a copy, you can pick a copy up at HistoricalFirearms.info/shop

US M1917s in British Home Guard Service

The transfer of rifles began in the autumn of 1940, with the training pamphlet ‘The Home Guard .300 Rifle P.17 (American Manufacture)’ published in September by the government. Which began “it now appears that all ‘Home Guards’ will ultimately be equipped with this rifle…”

In May 1941, the Home Guard’s .303 rifles began to be withdrawn and reissued to Regular Army units. These rifles were steadily replaced by American M1917s arriving from US stockpiles. This particular rifle was built by Remington in August 1918.

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M1917, right side (Matthew Moss)

By the spring of 1942, 80,000 M1917s had arrived, the first of 500,000 that were to be transferred. These would go some way to arming the over 1 million Home Guard members who needed weapons.

The Home Guard were stood up in May 1940, initially known as the Local Defence Volunteers, they were a sort of armed citizen militia made up of men ineligible for regular military service. They were formed into local platoons and companies and were initially poorly armed and equipped. But in time became a well-equipped home defence force.

The M1917 has a somewhat complicated origin. The story began with the British Army’s pre-World War One attempts to replace the SMLE. The Pattern 1913 was developed, based on a modified Mauser action and chambered in a new .276 round. Before the P13 could be fully evaluated and adopted – war were declared – and the British government placed contracts with US manufacturers to produce the Pattern 1914, the P13 adapted to chamber the standard .303 round. Due to a lack of parts interchangeability between the P14s which reached Britain it did not see front line service. In 1917 the US entered the war and found themselves in need of rifles quickly. With the production lines for the P14 already in place at Winchester, Remington and Eddystone the decision was made to produce the P14 chambered in .30-06. This was adopted at the Model 1917.

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.303 Pattern 1914 Rifle (Royal Armouries)

The per unit manufacturing cost of the US M1917 rifle in 1917-18 was only $26.00, they almost certainly cost Britain much more to purchase in 1940. Despite the M1917s being more plentiful in 1918, than the M1903 the US Army opted to retain the M1903 as their primary service rifle. As such the rifles sold to Britain had been in storage, often in cosmoline, for two decades and were in good shape.

As the M1917 was chambered in .30-06, or as the British referred to it .300, the rifles were painted with a red band around the wooden forend furniture to prevent the wrong calibre being used. The same measure was taken with the various Browning M1917 medium machine guns and M1918 Automatic Rifles also chambered in the American round. Some rifles also had a .300 stencilled on the butt.

Home Guard riflemen were to be each issued with fifty rounds of .300 ammunition, but in the early stages of the war ammunition was extremely limited. While this hindered familiarisation with the rifle somewhat, it didn’t hinder rifle training completely as many Home Guard units would have practiced with .22 rifles on miniature ranges and with rifles and ammunition provided at Regular Army Ranges. In this clip from some footage of Warwickshire Home Guard men, we see a corporal happily posing with a .22 Martini rifle.

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Home Guard on parade with M1917s (Imperial War Museum)

The M1917 is an excellent rifle and the Home Guard were lucky to have them. While those lucky enough to have received an SMLE may have been disappointed when they were given an American rifle in its place many appreciated the rifle. It was certainly better than the smattering of shotguns, civilian rifles, older service rifles and Canadian Ross rifles some units found themselves armed with during the Home Guard’s early days.

One Home Guard Unit In Denbighshire, Wales was initially issued 100 Canadian Ross rifles between 500 men until, in the spring of 1941, they received M1917s. One rifle for every two men.

Clifford Shore, a member of the Home Guard who later became an officer with RAF Regiment, recalled in his post-war memoir that the M1917s:

“were really splendid weapons; I never came across a bad one. In certain quarters they were not popular, but that can be primarily and summarily dismissed with the one word ‘ignorance’. …The higher velocity .300 cartridge gave slightly improved ballistics than the .303 cartridge in the P14, and I should say that the M17 was probably the most accurate rifle I have ever used.”

The Warwickshire Home Guard In Action

The video features footage of a Warwickshire Home Guard unit. In it we get a rare glimpse at the men at the range with their M1917s. They’re paired up with spotters and instructors and we also get to see the men in the butts running the targets for the shooters. 

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Home Guard at the range (Imperial War Museum)

In another piece of footage of the same Home Guard platoon we see them drilling with their rifles. they’re carrying out muscle exercises. The manual for the ‘.300 Rifle P.17’ lays these out.

The 1st practice trained men how to lift the butt of the rifle into their shoulders and how to level the rifle quickly for aiming. The second was to strength the grip of the hands and the 3rd laid down in the manual trained the soldier to hold the rifle steady while aiming building strength to increase stability.

Examining The M1917

The rifle weighs 9.2lbs (or just under 4.2kg) unloaded, it was 46.25in (117cm) long and had a fixed, internal double stack magazine, which because of the lack of a rim on the .30-06, could hold 6 rounds.

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M1917, left side view, action open (Matthew Moss)

The rifle has a Mauser-style bolt release on the right, pull back on that and slide the bolt out. The rifle has an aperture rear sight, zero’d for 200 yards, with a peep also mounted on a ladder giving graduations out to 1,600 yards.

The bolt of course has the dog-leg handle which was carried over from the P14, which in turn emulated the SMLE’s bolt handle position – falling nicely under the hand.

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Close up of the M1917’s receiver (Matthew Moss)

Unlike the earlier P14, the 1917 dispensed with the volley sights seen on the British rifles. The action is cock on close and the bolt itself is based on the Mauser 1898’s.

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M1917, right side view, action open (Matthew Moss)

This rifle was manufactured by Remington in August 1918. By the end of production Remington along had produced 545,541 rifles. At peak output almost 10,000 rifles were being produced per day, with the final number built standing at 1,727,449.


Specifications:

Overall Length: 46.25in (117cm)
Barrel Length: 26in (66cm)
Weight: 9.2lbs (4.2kg)
Action: Bolt-action
Capacity: 6-round internal box magazines
Calibre: .30-06


If you enjoyed the video and this article please consider supporting our work here. We have some great perks available for Patreon Supporters. You can also support us via one-time donations here.


Bibliography:

Britain’s Final Defence: Arming the Home Guard, 1940-1944, D. Clarke (2016)

With British Snipers to the Reich, C. Shore (1948)

Bureaucrats in Battledress, H. Smith (1945)

The U.S. Enfield, I. Skennerton (1983)

My New Book on the PIAT is Out Now!

I’m very excited to say that my second book has been published! It looks at the much maligned and much misunderstood PIAT – Projector, Infantry, Anti-Tank.

The book is available from retailers from the 20th August in the UK/Europe and the 22nd September in the US – but you can order a copy from me now regardless of location. I filmed a short video to show you the book and talk a bit about the process of writing it, check that out above.

The PIAT was the British infantry’s primary anti-tank weapon of the second half of the Second World War. Unlike the better known US Bazooka the PIAT wasn’t a rocket launcher – it was a spigot mortar. Throwing a 2.5lb bomb, containing a shaped charge capable of penetrating up to 4 inches of armour. Thrown from the spigot by a propellant charge in the base of the bomb, it used a powerful spring to soak up the weapon’s heavy recoil and power its action.

With a limited range the PIAT’s users had to be incredibly brave. This becomes immediately obvious when we see just how many Victoria Crosses, Military Medals and Distinguished Conduct Medals were awarded to men who used the PIAT in action. 

The book includes numerous accounts of how the PIAT was used and how explores just how effective it was. I have spent the past 18 months researching and writing the book and it is great to finally see a copy in person and know it’s now available.

The book includes brand new information dug up from in-depth archival research, never before seen photographs of the PIAT in development and in-service history and it also includes some gorgeous illustrations by Adam Hook and an informative cutaway graphic by Alan Gilliland.

If you order a book directly from me I’ll also include this custom illustrated postcard with a design featuring a PIAT and the famous line from A Bridge Too Far.

It’s immensely exciting to know the book is out in the world for all too enjoy. If you’d like a copy of my new book looking at the PIAT’s design, development and operational history you can order one directly from me here!

Me, bringing up the PIAT…

Thanks for your support and if you pick up a copy of the book I really hope you enjoy it! 

– Matt

SOE Sabotage – The Limpet Mine

During the Second World War Britain’s Special Operations Executive (SOE) developed a whole series of sabotage devices for use behind enemy lines. Using unique archival footage this series of short videos examines some of the weapons developed for use by SOE agents in occupied Europe. In this episode we look at one of the numerous version of the magnetic Limpet Mine developed by SOE and other clandestine organisations.

In this very rare footage we see a Free French Air Force officer, possibly training as a member of the SOE, place a limpet mine on a substantial piece of metal plate.

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Free French officer attaching a Limpet to a steel plate (IWM)

The mine seen in the footage is clearly much smaller than the Limpets used against ships. The Limpet mine was developed by Military Intelligence (Research) in late 1939-40. Stuart Macrae and Cecil Vandepeer Clarke developed a mine with enough magnetic strength to attach an explosive charge to the hull of a ship. The initial design seen here was quite large but the design was refined as the war went on with various types and marks. Here’s a Type II limpet, a MkIII and here is a Type 6 MkII.

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Limpet MkIII (U.S.N.B.D.)

The idea was that divers or saboteurs in small boats could quietly attach the mines to enemy shipping while at anchor. However, the usefulness of magnetic charges was clear and it appears that smaller versions, like that we see in the footage here, were developed for use against armoured vehicles and other substantial armoured targets.

Placing_limpet_mines.jpg
A demonstration of the Limpet mines and mine carrier (UK National Archives)

It’s unclear from the film what the explosive charge was, how big it was or how it was laid out inside the mine but from the damaged plate displayed at the end of the footage it may have been a ring of plastic explosive held in place by the four magnets. This would blow the characteristic round hold in the plates.

Interestingly, the limpet mine seen in the film is very similar to a Japanese design, the Type 99 anti-tank mine, however, it has a different fuse design and the four magnets are blocky rather than rounded. Whether the Japanese magnetic mine influenced this design developed by SOE is unknown.

Type 99 Magnetic Mine
Japanese Type 99 anti-tank mine (IWM)

I’ve been unable to find out these mine’s designation, it may not have been given one but it does appear to be fairly well developed. In this photograph we can see that a metal plate carrier has been developed to allow a soldier to carry 4 mines on his back. Perhaps these mines were developed for a specific mission. The magnetic Clam charge, which we have covered in an earlier video, would have done a similar job for smaller task


If you enjoyed the video and this article please consider supporting our work here. We have some great perks available for Patreon Supporters. You can also support us via one-time donations here.


Bibliography:

World War II Allied Sabotage Devices and Booby Traps, G.L. Rottman (2006)

SOE’s Descriptive Catalogue of Special Devices and Supplies, (1944)

SOE’s Secret Weapons Centre: Station 12, D. Turner (2007)

SOE: The Scientific Secrets, F. Boyce & D. Everett (2009)

British Land Mines and Firing Devices, U.S.N.B.D. (1945)

The footage is part of the Imperial War Museum’s collection © IWM MGH 4324 and is used under the Non-commercial Use agreement.

SOE Sabotage – Rail Charge

During the Second World War Britain’s Special Operations Executive (SOE) developed a whole series of sabotage devices for use behind enemy lines. Using unique archival footage this series of short videos examines some of the weapons developed for use by SOE agents in occupied Europe. In this episode we look at how rail track could be destroyed by plastic explosive.

Destroying railway infrastructure was a key mission for the Resistance groups and SOE agents active in occupied Europe. Numerous methods of damaging or destroying railways were developed, including Exploding Coal, which we have covered earlier in this series. In this 16mm colour footage, believed to have been filmed in 1940, we get an early look at the methods the SOE were developing to destroy track. The ultimate aim was to derail the locomotive and wreck the train with minimal effort and explosive.

In the footage we see two charges have been placed on the piece of track, with detcord attached to both. A soldier, with what appears to be a lever-action Winchester 94, is then seen taking aim. It seems he’s aiming at a striker board attached to ignite the detcord. He fires, we see a puff of smoke and a second later the charges detonate.

The footage then cuts to several men collecting the debris of the shattered piece of track. The track appears to have two large chunks blown out and the top edge, between the two charges, completely blown off.

An early SOE demonstration with the charges set on the rail (IWM)

Later in the war more testing was done and more refined techniques were developed. In their book SOE: The Scientific Secrets Boyce & Everett note that trials of devices and techniques for destroying railway lines carried out at Longmoor where the British Army had extensive sections of track and samples of rails used in different European countries. Trials to find the right quantity and positioning of explosive charges were carried out in late December 1943, these tests would inform later operations.

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Fog Signal Igniter (SOE’s Descriptive Catalogue of Special Devices and Supplies)

The SOE’s Descriptive Catalogue of Special Devices and Supplies includes a pair of illustrations demonstrating two methods of laying and detonating these charges. A so-called ‘French’ method with a pair of what the catalogue terms ‘Igniters, Fuze, Fog Signal, MkIA’ ahead of the charges in the direction the train was expected from. The train would crush these Fog Signals firing them and igniting a length of detcord linked to a pair of 3/4lb explosive charges fixed to the track as we see in this film.

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Polish Rail Charge layout (SOE’s Descriptive Catalogue of Special Devices and Supplies)

The alternative ‘Polish’ method had the same sized and located explosive charges but placed a Fog Signal either side of the charges to ensure that no matter which direction the train came from the charges would be detonated. This method was used on single track stretches of railway. Both of these methods were rated to ‘remove about one metre of rail.’

In this photo we see a member of the French Resistance setting an explosive charge on a railway line. While likely a posed photo we do see the pair of Fog Signals which will stet the charge off. These photographs show a pair of trains reportedly derailed by explosive charges.

Déraillement-16-avril-1942-AIRAN
A derailed French train c.1942 (AIRAN)

Boyce & Everett in their book SOE: The Scientific Secrets suggest that as many as 48,000 ‘Railway charges’, presumable a kit, were produced by the SOE. From the footage we can certainly see this method of destroying rails was effective.


If you enjoyed the video and this article please consider supporting our work here. We have some great perks available for Patreon Supporters. You can also support us via one-time donations here.


Bibliography:

World War II Allied Sabotage Devices and Booby Traps, G.L. Rottman (2006)

SOE’s Descriptive Catalogue of Special Devices and Supplies, (1944)

SOE’s Secret Weapons Centre: Station 12, D. Turner (2007)

SOE: The Scientific Secrets, F. Boyce & D. Everett (2009)

Arthur John G. Langley’s Unpublished Memoir (1974)

Footage use is part of the Imperial War Museum’s collection © IWM MGH 4324 & 4325 and is used under the Non-commercial Use agreement.

SOE Sabotage – Plastic Explosive

During the Second World War Britain’s Special Operations Executive (SOE) developed a whole series of sabotage devices for use behind enemy lines. Using unique archival footage this series of short videos examines some of the weapons developed for use by SOE agents in occupied Europe. In this episode we look at the component which made so many of them possible – Plastic Explosive. This video contains demonstrations of various uses for the malleable explosive.

The footage, believed to have been filmed in 1940, is part of the Imperial War Museum’s collection, it shows plastic explosive being demonstrated in a number of different applications. It was filmed by Cecil Vandepeer Clarke, a British engineer and sabotage expert who was a member of the Special Operations Executive and worked at a number of weapon research and development centres during the war.

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Plastic explosive and its effect (IWM)

The clip features a number of men preparing and shaping plastic explosive charges, adding fuses and detonators.  The explosive is then seen being applied to a steel plate in a ring shape, before being detonated. The resulting explosion punches a round hole through the plate. The film also includes demonstrations of what plastic explosive pressed against a tree trunk can do. Once detonated the roughly 1 foot thick trunk is splintered in two. Metal girders are also shown being prepared with a substantial block of explosive being pressed into its seams.

The SOE’s 1944 Descriptive Catalogue of Special Devices and Supplies lists the ‘Standard Charges’ of 1.5lbs or 3lbs of plastic explosive with an integrated central primer available in rectangular blocks inside a rubberised fabric. Of course SOE agents were taught to use as much or as little explosive as was needed for the task and they were taught to be able to improvise in any given situation.

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A standard 3lb charge, (SOE’s 1944 Descriptive Catalogue of Special Devices and Supplies)

Given the date of the footage the explosive being used is likely and early form of plastic explosive produced at Woolwich arsenal, possibly PETN or Cyclonite better known as RDX, which would have been mixed with a plasticiser to make the explosive malleable. 


If you enjoyed the video and this article please consider supporting our work here. We have some great perks available for Patreon Supporters. You can also support us via one-time donations here.


Bibliography:

World War II Allied Sabotage Devices and Booby Traps, G.L. Rottman

SOE’s Descriptive Catalogue of Special Devices and Supplies, c.1944

SOE’s Secret Weapons Centre: Station 12, D. Turner

SOE: The Scientific Secrets, F. Boyce & D. Everett

Arthur John G. Langley’s Unpublished Memoir (1974)

The footage is part of the Imperial War Museum’s collection © IWM MGH 4523, 4524 & 4325 and is used under the Non-commercial Use agreement.

SOE Sabotage – Magnetic Petrol Tank Bomb

During the Second World War Britain’s Special Operations Executive (SOE) developed a whole series of sabotage devices for use behind enemy lines. Using unique archival footage this series of short videos examines some of the weapons developed for use by SOE agents in occupied Europe. In this episode we look at an explosive magnet bomb, designed to be attached to any magnetic surface and detonate to destroy machinery or vehicles. It later evolved into the small pocket-sized ‘Clam mine’.

Today, we’re lucky enough to have some colour footage showing the of testing of a magnetic bomb which could be attached to the petrol tank of vehicles. The footage comes courtesy of the Imperial War Museum.

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A still from the footage showing the charge placed on the body of the car (Imperial War Museum)

From the film we can see that the bomb consisted of a small block of plastic explosive, a pair of strip magnets (or possible a horseshoe-shaped magnet) and a Switch No.10 time pencil delay detonator. The explosive block itself looks to be slightly smaller than the SOE’s standard 1.5lb charge.

In the film we see the bomb placed on the boot (or trunk) of a saloon car before various civilians and a corporal experiment with various ways of covertly attaching the bomb to the underside of the car. At one point the corporal allows himself to be dragged along behind the vehicle before making his escape.

Luckily the 16mm footage, filmed by Major Cecil Clarke, also shows us the effect of the explosive charge mounted on a petrol tank full of fuel. According to the details listed for the film by the Imperial War Museum the footage was filmed in 1940, at SOE Station XVII, located at Brickendonbury House in Hertfordshire.

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A still from the footage showing the bomb’s magnets (Imperial War Museum)

This configuration of the bomb doesn’t appear in the Special Operations Executive’s Descriptive Catalogue of Special Devices and Supplies published in 1944. However, Colonel Leslie Wood, Station XII’s commanding officer, described the demonstration put on during a visit by Brigadier Robert Laycock of the Commandos and William Donovan, the head of the American OSS in June 1942. One of the scheduled demonstrations was the “Effect of small ‘magnet’ charge of explosive on petrol tank of car.”

It appears that this ad hoc magnet charge evolved into ‘the Clam’, which was a smaller, version of the magnetic Limpet mine. The Clam evolved through a number of marks with the MkI having a stamped sheet metal casing and the later MkIII using a bakelite, plastic casing.  Both were made up of a plastic explosive charge inside a rectangular, rounded case with a pair of magnets at either end. They were detonated by either a Time Pencil or an L Delay fuse attached to a No.27 detonator. The MkIII had 8oz (226g) of high explosive filler, such as TNT/Tetryl 55/45.

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MkIII Clam (Imperial War Museum)

While unlike the larger Limpet they weren’t developed for under water use but the Clam could be mount onto any vaguely flat magnetic surface including engine blocks, fuel tanks, crank cases, cylinder blocks, rail tracks and steel plate.

At just 5.75” x 2.75” x 1.5” they were easily concealable, could be carried in a pocket and were non-descript enough not to draw attention. An estimated 68,000 Clams were made under supervision at Aston House according to Des Turner’s book on Station XII.


If you enjoyed the video and this article please consider supporting our work here. We have some great perks available for Patreon Supporters. You can also support us via one-time donations here.


Thanks David Sampson of www.millsgrenades.co.uk for the use of his photo of the cutaway Clam.

Bibliography:

World War II Allied Sabotage Devices and Booby Traps, G.L. Rottman

Technology and the Civil War, S. Mountjoy & T. McNeese

SOE’s Descriptive Catalogue of Special Devices and Supplies, c.1944

SOE’s Secret Weapons Centre: Station 12, D. Turner

SOE: The Scientific Secrets, F. Boyce & D. Everett

The footage is part of the Imperial War Museum‘s collection © IWM MGH 4325 and is used under the Non-commercial Use agreement.