Standing Well Back
1910-1920

This man made IEDs that blew up dozens of British trains

Thanks to “JB” for flagging up an interesting report of an ordnance officer dealing with a German IED in East Africa using “hook and Line” techniques during WW1. It’s led me down a fascinating burrow, and ties up a whole series of IED attacks on trains and other targets. It also provides a dreadful familiarity – an IED campaign with direct parallels to modern IED attacks in Iraq and Afghanistan, and it sits in the context of a part of WW1 that I was barely familiar with. Here’s the story followed by the links and its context in IED history.

This man is Nis Kock. He was a young sailor in the German Navy. He made literally hundreds and probably thousands of IEDs for the the German East African Campaign in WW1.  He is often described as a Danish sailor, but he certainly saw himself as German, although he could speak Danish as well as German.  He was already a member of the German Navy in 1914 when he was recruited for special duties.  The Germans were putting together a blockade runner, a ship disguised as a Danish freighter to slip through the British blockade in the North Sea and resupply the cruiser Königsberg off the East African coast. As a young adventurous man, he jumped at the chance.  His ship, a captured British steamer the “Rubens“, was called the “Kronborg” for the purposes of the mission, loaded with coal, dynamite, field guns and ammunition. It slipped through the blockade in late February 1915, sailed the Atlantic and round to the Indian Ocean coast of East Africa. There the Königsberg was being blocked by British cruisers in the Rufiji delta. At the time there was also a land campaign beginning between the British and the German Forces in East Africa under the command of General Lettow-Vorbeck – a remarkable character. I dont have space to describe this campaign but suffice to say that a few thousand German forces tied up a quarter of million British Empire troops for the duration of the war, who might otherwise have been deployed to the Western Front.  It was a nasty, vicious campaign fought in appalling conditions in the jungle and the bush. What is little known, I think, is the key role that IEDs played in restricting British movement in the theatre. Certainly the use of explosive devices or mines is barely mentioned in British history but it is clear they were fundamental to Lettow-Vorbeck’s successful strategy, operations and tactics.

When the Kronborg arrived off the coast of East Africa it raised the suspicions of the British Royal Navy, spotting it as it tried to break through their screening blockade, and chased it into the shallow water of Manza Bay (nowadays in Northern Tanzania). The ship was damaged by naval gunfire, and scuttled with just her superstructure remaining above water while the crew escaped ashore. Importantly the cargo received little damage and the British didn’t realise this. Over subsequent weeks, Nis Kock and his fellow crew members recovered most of the cargo from the semi-submersed Kronborg, and much of this material became Kock’s raw materials for IED manufacture in subsequent months and years.

What happened next is interesting. The Kronberg’s pseudo-Danish crew (actually German) were co-opted into the German East African Force. Nis Kock, clearly a bright individual was made assistant to the “munitions director”. His task was to store the explosives and munitions and prepare them for use. Keen readers of this blog will recall the following earlier posts:

  1. The use of firearm mechanisms for explosive device initiation.
  2. How trigger mechanisms were used by the Boers in the Boer War to initiate explosive devices atacking British trains

Now it appears that there were a number of Boers, veterans of the war against the British in South Africa a decade and a half earlier. They clearly remembered the technique of using an upturned trigger mechanism as a switch to initiate the explosives in a device. Kock was instructed to manufacture such devices and he got to work.

Here’s a reminder of the Boer device:

It would appear from Kock’s diaries that he perhaps wasn’t aware of the origins of this concept, but he certainly churned them out as packages for the raiding German insurgency to deploy, probably in their hundreds.  It’s clear to me that they were key and central to Lettow-Vorbeck’s plans as Kock received constant requests to produce more.  He was operating either from makeshift workshops or “in the field’ and developed, I think, remarkable skills.  The impact of the IEDs made by Kock was considerable, for example in the summer of 1915, Lettow Vorbeck turned his attention to the Ugandan railway – which ran through what is now Kenya and was a key logistical route for the British. The German insurgency (and that’s what it absolutely was) had considerable success with their IEDs. For example in one short period between March and May 1915, the German insurgents using IEDs blew up 32 British trains, nine bridges and a dam. I believe that these could have all been devices made by Nis Kock.

Kock himself occasionally laid his improvised mines. His experience indicated to him that setting the device was somewhat tricky with the bomb-layer having to reach into the buried device to release the safety catch on the device once it was in position and he describes in his diaries that as a consequence he developed a new design that made the process safer and easier. Regrettably there are no details of this design change.

Kock used a variety of components – usually the initiation switches were the trigger mechanisms from damaged firearms, used either as booby traps or as pull switches for demolitions.  I suspect there was a shortage of “detonators/blasting caps” and there were no batteries to use electrical initiation methods so this got around that problem with the damaged firearm firing a bullet into a main charge of dynamite or an adapted shell fuze. But I am guessing a little here, as Kock deliberately is a little vague on detail in his notes. The main charge was either dynamite recovered from the Kronborg, ammunition intended for the Königsberg in terms of naval gun shells or captured munitions.  The devices were used against trains but also as demolition charges and to emplace on tracks used by the British in the bush, placing a wooden board on top of the trigger and lightly covering the board with sand and earth. Here’s a translated excerpt from his diaries:

 

As I researched the context of this insurgency and its use of IEDs I was struck often by the similarity between the activity of Lettow-Vorbeck’s guerrilla groups and more recent insurgent IED campaigns in Iraq and Afghanistan.  Von Lettow-Vorbeck’s remarkable campaign is worthy of closer study in that context.

Most of all, I am intrigued of a very weird parallel.  At the exact time that Kock was enabling Von Lettow-Korbeck’s campaign against the British in East Africa, exploding devices under trains on the Uganda railway initiated with rifle triggers, an idea from the Boer War, then an identical campaign was being waged in Arabia. Here, Lawrence of Arabia’s insurgent campaign against the Ottoman Turks and the Hejaz railway, was being enabled by Garland’s trigger-initiated IEDs, inspired too by the Boer war experience. See here and here. Same device, same war, different campaigns, different sides.

In terms of an EOD response, there appears to be very little detail.  Here’s the diary event which was sent to me which started off this pot.  In his War Diary, Major Guy Routh reports, “having to dissect these German contraptions for blowing up our train engines and although they learnt to put two trucks of stones in front of the engines, the enemy countered that with delay fuzes. It was no fun pulling a wire from behind a wall in case the bombs go off, nor was it a job that could be delegated”.  It should be noticed also that there was a little technological battle ongoing between the IED design and the countermeasures designed to defeat it – again this translates directly to much more recent experience in recent wars. However new we feel these modern IED threats are, they have almost always been seen before, it’s just that history is always forgotten.

Update: Some more detail of the attacks:

Here’s two photos showing that bridges were blown up:

 

 

I have also found a report that the Germans (probably Kock) made improvised command-detonated sea mines for use at the coast, however none functioned as intended. For attacks on tracks against foot patrols and vehicles, it appears that as well as the wooden board method, the trigger mechanisms were adapted to function by trip wire.

My friend Ian Mills, who has investigated the Boer use of these devices in the earlier Boer conflict reminded me that the British used the counter-IED method of pushing two sand or rock loaded carriages ahead of the train as sacrificial elements against Boer IEDs, so the British re-used this technique here. The Germans claim to have developed a mechanism that would “count” the number of wheels that passed over, so circumventing this counter-measure. Regrettably I have no detail of this.

It also appears that the most effective IEDs were actually made from British demolition charges, captured by the Germans at Tanga.

20th Century

Chemical render-safe techniques for explosives -1926

I’m deep into research into Soviet explosive activity in the first half of the twentieth century but in doing so came across a very interesting Russian technical EOD procedure from 1926, developed at an incident that’s worth discussing.

In many parts of the world in the late 19th and 20th century, bridges were built with special shafts, or alcoves, designed to take explosive charges to destroy the bridge in the event of a foreign invasion as part of defensive blocking operations.  At one point in about 1926, a bridge in the Ukraine was being inspected, and engineers found a forgotten series of explosive charges in a bridge, left over from a previous conflict. It is likely that in preparation for defensive operations that never subsequently occurred, the bridge was prepared for demolition by placing large quantities of explosives in the shafts, and then for whatever reason this was forgotten.

The large charges were of dynamite and had been placed in shafts built into a bridge then covered in a thick protective layer of grease.  Because of their age, and environmental heat cycling over the years, the dynamite was exuding nitroglycerine, and was assessed as very unstable.  The engineers were tasked with removing the dynamite without detonating it.

The innovative render-safe technique developed at the scene, if I’m honest, isn’t quite 100% clear because I’m dealing with a non-technical translation, but it’s interesting for a few reasons and was apparently successful.  It went like this, or something like this, from what I can glean.

  1. Oil (I think engine oil) was slowly poured onto the protective grease, dissolving it, but leaving behind the dynamite.
  2. The engine oil was then treated with sawdust, to soak it up from the bottom of the shaft and carefully removed. My guess is that such a shaft would have a drain hole, and this may have been plugged.
  3. A warm water-based alkaline solution was then poured onto the unstable dynamite.  This isn’t a technique I’m familiar with, but the engineer responsible claims the alkaline solution in contact with nitroglycerine results in a more stable material, which was then decanted from the bottom of each bridge shaft. I don’t know volumes or timescales but the whole operation dealing with several shafts, presumably one after another, took several days. It could be that the warm alkaline solution simply washed the remaining oil from the dynamite, as the engineer seems to be concerned with the grease interacting with the exuding nitroglycerine.
  4. Finally the remaining dynamite could be removed.

Have any readers come across any elements of this render safe procedure before? Any chemists out there able to comment on the nitroglycerine / alkaline effects and products? I’m assuming that some form of hydrolysis reaction takes place but my chemistry knowledge isn’t quite strong enough in this specific case… comments very welcome. Or was something lost in translation?

There is much more fascinating Russian stuff coming soon. The explosives specialist who came up with the procedure went on to be responsible for more explosive devices than any other person in history, and I’ll be posting more stuff on him soon. In the history of IED campaigns, and associated activity I don’t think there is a more important person.

Update:

Thanks to Matyas Koszik for this comment suggesting that chemically a hydrolysis of NG makes sense:

Re:alkaline hydrolysis of nitroglycerine:
https://onlinelibrary.wiley.com/doi/pdf/10.1002/kin.550160808
Seems to work similarly to other ester hydrolysis reactions.

 

Command IED

Command initiated explosive device from 1582

I’m steadily working my way through more military handbooks from the late 1500s when there appears to have been a lot of revolutionary thought going into military technology and explosive device development in particular. My previous post on a grenade was dated 1578, you may recall that Giambelli’s ship explosive device was 1584, and I’ve written before about a postal device in the city of Pskov in 1581.  I’ve also written before how “gun-locks” were used as initiating devices for explosives over a 250 year period.

On that latter point I’ve just found a gun lock (in this case a wheel-lock) drawn in a manuscript from Germany, dated 1582. The drawing is here and as you can see the design is very clear.

 

The wheel-lock was a progenitor of the flintlock which came in a few years later, in about 1600. In a wheel-lock a spring-loaded wheel spins against some pyrites held in the cock.  Here you can see how the gun lock has been removed from a firearm and fastened to a frame. A string is attached to the trigger, led around a pulley and away to the person initiating the device. When the target presents itself, the person pulls the string, which pulls the trigger. On pulling the trigger a spring mechanism spins the steel wheel against the pyrites held in the cock. This causes sparks which ignites the fuse. The fuse leads to a barrel of gunpowder hidden nearby.  In a post a few years ago I have an image showing a multiple IED attacks against a military convoy employing these exact devices, so it’s good to corroborate the attack with a contemporary IED design.

So, this is another example of how explosive device design appears to have developed rapidly at this peculiar point in history, across Europe. I think it is the publication of these handbooks and manuals of military science that seems to be helping – bu I’m afraid I’m not a good enough historian to identify other causes of this bubble of ideas. Comments from proper historians welcome!

A couple of follow-up thoughts:

1. The “pull string” could of course be adapted to a trip string, turning the command-initiated device into a victim-operated booby trap.

2. One possibility of the sudden uptick in apparent use of explosive devices at this point in history is manufacturing technology.  I wonder of clock-making saw similar technological leaps at this time.  Wheel-locks were invented in the early part of the century but are quite complex in design from an engineering and manufacturing perspective. Perhaps clock making manufacture and design took parallel leaps at this time and the transfer of ideas to wheel locks (essentially a clockwork mechanism, with a wheel powered by a spring) enabled cheaper device components and they became more commonly available rather than the early wheel locks which were the weapons of the rich.  I’ve just read that coiled carbon steel spring (essential for wheel locks) was first made possible in the early 1500s – perhaps manufacture became easier in the 1570s, allowing them to be more easily and cheaply manufactured, and hence available for regular soldier’s weapons and “one-time use” in explosive devices. Perhaps the wheel lock mechanisms, like in the diagram above, were separated from the main charge and were thus in theory recoverable after the event.

19th Century

Earlier Russian stay-behind explosive devices

In my previous post I discussed Russian stay-behind explosive devices . Now, it is usually my habit to dig back in history to find earlier instances of certain attack styles, and indeed this does apply in this case. I’ve written a little before about Russian mines in the Crimea during the war with the French and British in the 1850s. When the Russians lost Sebastopol to the British and French in 1855, they “left behind” numerous booby-trapped explosive devices hidden in the buildings and connected, in some cases, to powder magazines within the fortresses of Sebastopol. So these were massive IEDs, left behind within potential military facilities, by the Russians. so in some ways exactly the same concept of operations as the WW2 F-10 devices, except the latter were command detonated rather than victim-operated.

Here’s a report from a “war artist” who was on the scene of one of the explosions:

Yesterday, as I was sketching in the west of Sebastopol, an explosion shook the buildings around and reverberated through the roofless and untenanted edifices of the place. The Arsenal Creek was filled with a heavy black smoke, and showers of large stones fell into the water, lashing it for a moment into sheets of foam. The centre of the fire was a battery on the left flank of the Creek Battery. This was one of the works erected by the Russians to sweep the approaches of the Woronzoff road; it was built of stones taken from the houses around it, faced with earth externally, and without a ditch. The magazine was in the foundations of a house which had once stood there […]. The Russians had placed a fougasse over it, and an accidental tread upon a wooden peg driven into the earth broke a glass tube of inflammable matter which communicated with the powder below […].

Three of the men in the work were blown to atoms; and a large number were buried in the ruins; whilst sad havoc was at the same time committed on parties of workmen leading mules along the road close by. Two soldiers of the guard in the Creek Battery were killed by stones projected with great violence into the air, and launched with fatal force upon them. Several mules and horses were killed in this same manner, and every point within 200 yards of the spot was visited by the terrible shower. The crater left by the explosion was about twenty feet deep and twenty wide; and in its crumbled sides were found some of the wounded, who were speedily conveyed to hospital.

So for the victors in urban environments, the challenge of stay behind devices goes back a long way. I contend that there are direct similarities in the concept of operations between the Russian stay-behind devices in the Crimea in 1855 and those of 1941 and the Eastern Front. I wonder too about those towns in Iraq and Syria, liberated from ISIS/Daesh and the identical challenge faced by EOD teams this very day and for years to come. Nothing in EOD is new.

From the description above it’s clear that these were versions of the Jacobi-Fused landmines used elsewhere in defensive positions by the Russians.

The fact we know a fair amount about these mines is in part due to a US military mission to the Crimea.  In 1855 Jefferson Davis, then Secretary of War, created a team called “The Military Commission to the Theater of War in Europe”.  The team consisted of three officers – Major Richard Delafield, (engineering), Major Alfred Mordecai (ordnance) and Captain George B McClellan of later US Civil War fame.  McClellan resigned in 1857 and the report was published in 1860. It is wonderfully detailed and I’d recommend it to any students of military history – it covers just about all aspects of European military developments, from defensive positions, artillery to mobile automated bakeries aboard ship, ambulance design, hospital design and French military cooking techniques.

With regard to innovative munitions, Immanuel Nobel (father of Alfred Nobel) had been engaged by a Russian military engineer,  Professor Jacobi,  to develop submarine charges and a contact fuzing system. These “Jacobi” fuzes consisted of a pencil sized glass tube filled with sulphuric acid fastened over a chemical mix.  Some reference history books say the chemical mix was potassium and sugar but I think that’s probably a misunderstanding – I would suspect the mix was actually potassium chlorate and sugar, as in Delafield’s report below.  When the glass vial contianing the acid is broken, (such as when stood upon) it mixes with the chemicals below and explodes initiating a gunpowder charge sealed in a zinc box.  One might have expected Mordecai to take an interest in the IEDs but it was Delafield who took particular interest and heartily recommended the use of such things by the US military. Here is an extract from Delafield’s technical report from the device recovered by the British:

They consisted of a box of powder eight inches cube (a), contained within another box, leaving a space of two inches between the, filled with pitch, rendering the inner box secure from wet and moisture, when buried under ground. The top of the exterior box was placed about eight inches below the surface, and upon it rested a piece of board of six inches wide, twelve inches long and one inch thick, resting on four legs of thin sheet iron (o), apparently pieces of old hoops, about four inches long. The top of this piece of board was near the surface of the earth covered slightly, so as not to be perceived. On any slight pressure upon the board, such as a man treading upon it, the thin iron supports yielded. When the board came into contact with a glass tube (n) containing sulphuric acid, breaking it and liberating the acid, which diffused within the box, coming into contact with chloride of potassa (sic) , causing instant combustion and as a consequence explosion of the powder.

Delafield goes on to note that the British and French exploiting these devices did not have a chemistry lab available to properly identify the explosives.  I think a mention of a lack of resources for what today might be called “Tech Int” is instructive! The deployment of Technical Intelligence laboratories and associated “CEXC” capabilities to theatres remains an issue today.

A second device is then described:

Another arrangement, found at Sebastopol, was by placing the acid within a glass tube of the succeeding dimensions and form. This glass was placed within a tin tube, as in the following figure, which rested upon the powder box, on its two supports, a, b, at the ends. The tin tube opens downwards into the powder box, with a branch (e) somewhat longer than the supports, (a, b)   This , as in the case of the preceding arrangement, was buried in the ground, leaving the tin tube so near the surface that a man’s foot, or other disturbing cause, bending it, would break the glass within, liberating the acid, which, escaping through the opening of the tin into the box, came into contact with the potassa, or whatever may have been the priming, and by its combustion instantly exploded the powder in the box.  What I call a tin tube, I incline to believe, was some more ductile metal, that would bend without breaking. For this information I am indebted to the kindness of an English artillery officer who loaned me one in his possession and from which measurements were made.

The famous Colonel Majendie, who later became the British Chief Inspector of Explosives, the UK first official bomb disposal officer, and who conducted remarkable IED and technical investigations some 30 years later, in the 1880s, fought as a young artillery officer at Sebastopol. Could it be the same man?  I’d like to think so.

The Jacobi fuse , or at least a variant of it, was used in Russian sea mines at the time – see this earlier post.

But of course one can go back further in time to look at previous Russian efforts, earlier still. When Napoleon’s Grande Armee entered Moscow in 1812, it was with great triumph and the summit of a remarkable campaign – but within a day Russian saboteurs had started to burn the city to make it uninhabitable for the occupants. Napoleon himself had to be rescued from fires encroaching the Kremlin and soon the retreat from Moscow started.  I don’t doubt that the Russians of 1855 and 1941 knew their history. and whether it is a knowledge of history, or something else, the ruins of Syria and Iraq today pose an identical challenge.  Moscow 1812, Sebastopol, 1855, Kiev and Kharkov 194, and Syria 2019.

Here’s a pic of Moscow burning, set fire by Russian saboteurs, with Napoleon looking glumly on.

Update:

I’ve been asked for a bit of clarity on the Russian mines discussed by Delafield and the “Jacobi fuzes”.

So, Jacobi fuzes were designed by Immanuel Nobel, and were fitted to a range of munitions. The fundamental principle behind the fuze is a glass vial of sulphuric acid held above a potassium chlorate (or potassium chlorate and sugar) mix.  Some action or other on the munition breaks the glass vial, which then allows the sulphuric acid to mix with the chlorate. this generates enough energy to ignite a powder train to the main charge.  In the sea mines encountered by the British Navy in the Baltic during the Crimean war there were steel springs and rods which broke the glass when a ship touched the moored mine.  In the Crimea itself and these devices above then it was the action of a person stepping on a plate which in turn caused the glass to break.

Delafield’s diagrams, (Fig 101 and 102) respectfully, are indeed not that clear. But there are two different mechanisms, both pressure from above in each device which cause the glass to be broken. The “pitch” mentioned is simply a method to seal the box containing a volume of gunpowder from the ingress of water from the ground in which it is buried, giving the “mines” a longevity. If you wish you can read the original “technical intelligence report” at this link here.

20th Century

Russian WW2 Radio Controlled Explosive Device

I’m afraid this is going to be a long and detailed post, but it is one of the most interesting historical explosive devices I have ever written about.  Despite the length, I must urge a little caution. I’m working from a very small number of poorly translated documents, about a technology that is at the edge of my understanding, and about which there are conflicting assessments and denials. I have some Russian references but my Russian is very poor and worse now through lack of use. Very happy for input from anyone who has a better handle on this or who sees errors in my analysis.

In the 1920’s and 1930’s the Russians developed a number of radio-controlled systems. As an aside, this included radio-controlled tanks.  Another system, and the subject of this blog piece, was the F-10 radio-controlled mine. This mine was first developed in 1929 (90 years ago!) and deployed operationally in 1941 in the “Great Patriotic War” (WW2) against the Germans, most notably in Kiev, Kharkov and Odessa, and against the Finns in what is called the “Continuation War”. Their use came to a real crescendo in September/October 1941.  There are several very interesting aspects to the device, – its design, its employment/and the MO of its use, the highly ambitious planning and significant operations it enabled, and the reprisals that resulted.  Furthermore, the electronic countermeasures employed by both the Finns and the Germans at great speed following technical exploitation of captured systems provide useful historical vignettes about rapid fielding of EW against radio controlled explosive devices.

By necessity, I have to get a little technical, and to repeat, some of my technical assessments and understanding might be wrong, but I’d like to get this out there rather than spend a year refining peculiar technological aspects.

So firstly, the design of the system.  Here’s an image of the main receiver (Rx) of the system. I think this image is actually German, following a render-safe procedure:

The receiver is a briefcase sized radio and decoder, and I’ll come on to the detail of that shortly. It is accompanied by, and wired to, a large battery. More pictures of the components (I think).

The radio component is the Left hand box, the right hand box is the power source or battery. The “decoder” is the small object to the front left.

Below there is a battery, a radio box, and the rubber bag in which the device is placed when concealed (usually buried) and what appears to be detonation cord or cables, perhaps leading to a large explosive charge.

Here’s an image of the batteries and radio enclosed in the rubber protective bag , ready for burial and concealment.

The system is designed to recieve a coded signal , and detonate up to three explosive circuits. The complete device, less explosives, weighs 35kg. There is a 30m antenna, which according to the references can receive a signal if the antenna, placed horizontally, is buried in the ground up to 120cm (some assessments say less),  in water of a depth up to 50cm or hidden by brickwork up to 6cm – Grateful for comments on this aspect from any EW experts or RF engineers.

The system has a complex timing system. Using the batteries alone would give an operational life cycle to the radio receiver and enable power to the explosive circuit of 4 days. But a mechanical timing system is integrated to give a complex range of operations, including a long time delay before activation or providing a number of time “windows”, from as short as 2.5 minutes “on” to 2.5 minutes “off”, and other longer on-off windows, giving a  maximum receiver power life of 40 days.  There is a complex relationship between the length of time windows and the length of the command signal required that I don’t fully understand.  Suffice to say, that several frequency signals in a sequential row need to be transmitted for the decoder to accept a command, and the length of those individual sequential signals isn’t quite clear to me, but is at least a minute and sometimes longer.

Additionally, there are some clever extras… It is possible to set a mechanical time delay to explosive initiation (avoiding the Rx) of up to 120 days. If I understand it correctly, this was usually set as a last-resort back-up self-destruct. It is a mechanical clock and some EOD successes were made by detecting the ticking clock. The explosive contents used with F-10 varied from a few tens of Kg to several thousand Kg.

The device also was fitted or could be fitted (I’m not sure) with anti-handling switches. The anti handling switches quoted in the spec are “EHV, CJ-10,CJ-35, CMW-16 and CMW-60” I haven’t investigated these yet but at least one is a pull switch attached to the opening of the rubber bag the system is deployed in.

The range of the command system of course depends on the power of the transmitter. From German exploitation of a captured F-10 device, the frequencies employed reportedly range from “1094.1 khZ to 130khz”. Again I welcome comment from EW specialists.  This implication is that the “setting” of each F-10 mine to specific frequencies was quite flexible and easy but I’m not sure quite how it was done.  Perhaps by replacing individual tuning forks?  I have found one reference, a Finnish technical exploitation report, saying the tuning forks were colour coded, which would be logical. Another report suggests that the radio receivers were marked with a numerical code in roman numerals, which defined the initiation frequencies.  A slightly contradictory early Finnish exploitation report, very interestingly, suggests that two of the frequencies allocated to the F-10 were set to pre-war popular music radio stations from Kharkhov and Minsk, with a specific “calling tune”.  I can’t quite make sense of that, but never mind.

The decoding system predates DTMF of course. A system such as the F-10 needs to be able to discriminate random signals from an actual command signal, so this system uses (I think) a triple tuning fork mechanism, with specific successive frequencies transmitted over a time window. Only when three successive signals of different specific frequencies, each of a sufficient duration, are received will the “AND” logic of the system allow initiation.

Such a capable system allows for a wide range of operational designs, or employment plans.  It is clear that the Russians used these in areas where they ceded territory, so they are “stay-behind” sabotage devices. They are expensive too, compared to other mines and challenging and resource-heavy to deploy effectively. So to justify that, the targets have to be significant. Initiation could be by a separate line-of-sight concealed engineer team using a transmitter quite close, or indeed could be several hundred km away (I think). So the device could be under observation and initiated at the optimum time, or more remotely, without line of sight, perhaps based on intelligence.

In the Finnish campaign, the Finnish military encountered quite a few of these devices as they re-took the city of Viipuri in September 1941 and rendered at least one safe. One such item is on display in a Finnish military museum. As a result, it is alleged, they developed an electronic counter-measure, which was to set up a permanent high power frequency transmission on one of the first two frequencies. This overwhelms the timer element of the decoder and perhaps jams incoming other frequencies from the system with its power. That, sort of, makes logical sense to me but I’d appreciate comment from any ECM experts. I have seperate reports, hard to confirm, that the “jamming signal” was a piece of music transmitted at high power over and over again at a fequency of 715KHz.  In response the Soviets changed the frequency of the F-10 systems. and the Finns responded by putting the same song out, constantly, on every frequency they could, apparently

Here’s an image of a Finnish EOD team and the F-10 recovered safely from a water tower in Vyborg. I’m pretty sure the “wall” they are leaning against is TNT blocks.


The removed radio controlled exploding device, wiring, 2400kg TNT and the Finnish engineers that found and removed the “mine” from Viopuri/Vyborg water tower

On a more practical level, Finnish engineers worked out that the long 30m antenna gave them an opportunity to locate the mine. In any places where they suspected a buried F-10, they dug a small trench 2 ft deep, around it, and if there was a mine hidden there, they invariably encountered the antenna.

As an aside, I understand that the young Finnish Officer (Lauri Sutela) who rendered safe one of these devices in September 1941 in Vyborg rose to be Chief of the Finnish Defence Forces in the 1980s.  There’s always hope then for young EOD officers to make their way in the world…

German EW responses to radio control initiation appear also to have been developed and deployed quickly. They captured an F-10 mine in mid September 1941 and it appears there were countermeasures deployed, apparently by 25 October at the latest. That’s pretty fast for a capture, technical exploitation to deployed countermeasure cycle.

German countermeasures included:

  1. Digging an exploratory trench looking for the antenna as the Finnish engineers did. Quite often Russian prisoners of war were used for this task.
  2. Use of an electrical listening microphone to listen for the mechanical clock component
  3. A responsive jamming capability to transmit, quickly, a powerful “blocking”  signal if any known F-10 frequencies were detected. I don’t think this was automated.
  4. There was another RF method developed, apparently of limited use, which involved transmitting a “disabling” signal, somewhere “between 150 – 700Hz” but I cant quite make out the sense of that. Again advice accepted, gladly.

When the Germans took territory from the Russians, in 1941, eventually the cities of Kharkov, Kiev and Odessa were ceded.

In the run up to Russian withdrawal from these cities, engineer teams in significant number laid a wide range of mines and booby-traps for the advancing Germans. The Russians worked out that quite often Germans would take over large buildings that had been used for Russian military headquarters, and use them for their own headquarters. It appears that although equipped with a wide range and number of relatively cheap mines and booby traps, the expensive radio controlled mines were used in a very focused manner to target senior officers and their staff in headquarter buildings. The Germans moved into large office buildings (as previously used by the withdrawing Russians), presumably because they had the scale, number of rooms and perhaps even telephone lines. So a vacated Russian Army HQ would become a HQ for the advancing Germans. This provided a predictability that the Russian engineers could exploit. Russian engineers became expert at laying “slightly obvious” booby traps which German EOD would render safe and then assume the ground underneath was clear – but actually often there was an F-10 radio controlled mine buried deep and everything including the antenna was much more carefully concealed.

In the captured cities of Kharkov, Kiev, and Odessa, German generals and their Headquarter staff were killed by concealed F-10 devices over a 7 week period in 1941, as follows:

Between 24 and 28 September, numerous F-10 devices were exploded in central Kiev in buildings occupied the prior week by German Army headquarters.  The F-10 devices were allegedly initiated by command from stay-behind hidden engineer units observing the area from an island on the Dneiper river. In particular an explosion on 24 September hit the Rear Headquarters of the Wehrmacht army Group south killing a large number of officers, including the artillery commander of the 29th Wehrmacht Corps. In immediate reprisals the massacre of Babi Yar took place, with a death toll of 100,000.

On 22 October, the Romanian Military Headquarters in Odessa, established 3 days earlier and manned jointly by Nazi and Romanian military staff was exploded up by an F-10 device (I believe) killing 67 people including the Romanian General. 40,000 Jews were killed in reprisals.

On 14 November, multiple buildings just occupied by German forces in Kharkov were destroyed I think with F-10 devices. There were hundreds of casualties, including the German commander, Generalleutnant Georg Braun. In immediate reprisals 200 civilians, mostly Jews, were hung from balconies of surrounding buildings. The following month there were further reprisals and 20,000 Jews were gathered at the Kharkov Tractor Factory. All were shot or gassed in a gas van over the next two months.

It is hard to get to the bottom of how many F-10s were used in these cities but I think they were used in significant numbers, alongside extensive conventional mining and booby trap techniques. I think historians in regarding these cities separately in the Eastern front campaign miss the point that this was a clear strategic effort to deploy these weapons to “cut off the head” of the advancing German armies. The fact that these attacks came at the same time as their use in the Vyborg peninsula against the Finns, cannot be a coincidence and I sense a strategic decision to employ these weapons as the Soviets were being pushed on all fronts.  In the main, use of the F-10 was part of operations under the command of a remarkable explosives engineer, Col Ilya Starinov.  I will be returning to discuss Starinov in future blog posts, suffice, for now, to say he was ultimately responsible for more explosive attacks on trains and railways than any other man that has ever lived (by a long way) and fought in at least 4 wars as a Russian explosives expert. He really was the instigator of Soviet Spetznatz tactics.

This F-10 radio controlled device then poses a fascinating case study of an early radio controlled explosive device threat, and how a technical capability (in this case of a pretty flexible system) when coupled with intelligence and innovative employment can pose significant threats not only to whatever troops are in its path, but also targeted specifically on high value enemy leadership as part of a strategic plan.  The appalling reprisals to these F-10 attacks suggests the concern felt by the Wehrmacht.

This story also demonstrates the rapidity that is possible with suitable technical intelligence resources and processes to develop both technical and procedural countermeasures. The RC threat and response game is nothing new.

 

Update:

I’ve been looking further into how the F-10 radio controlled mine was designed.   In itself it is an interesting story.  In 1923, the Soviets started up a “Special Technical Bureau” for “Military Inventions of a Special Purpose” known as “Ostekhbyuro” in typical Russian fashion.  The two people credited with the invention were V. Bekauri and V Mitkevich. Bekauri, was instrumental in developing a number of other Soviet radio controlled systems including the Teletank and other guided weapons. I believe the work on the F-10 mine was completed in 1929. In 1932 the devices were taken on by a specially constituted military Unit, I think designed to exploit the specific capabilities of these devices. The radio controlled mines were at first referred to as “BEMI” mines, named after the first two letters of the last name of each inventor. Later they were re-designated F-10.

In 1937, Bekauri had risen to be Director of the Ostekhbyuro, but was arrested, interrogated, charged with counter-revolutionary behaviour, found guilty 15 minutes later and then executed as part of Stalin’s purges in 1937.

 

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