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. We begin the series with a look at the history and development of Explosive Coal. Explosive coal was designed to explode inside fireboxes, furnaces and coal stores hampering enemy infrastructure.
I came across this footage while doing some research in the Imperial War Museum’s online catalogue. This piece of 16mm film 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 including MD1 at Whitchurch and SOE Station XII at Aston.
SOE or Special Operations Executive were a clandestine force tasked with conducting irregular warfare behind enemy lines including sabotage, assassination, intelligence gathering an small scale raiding. One of the sabotage methods developed was introducing an explosive charge into the boiler firebox of a ship or a locomotive or a power station or factory’s furnace. This achieved by disguising the explosive as either a piece of fuel like coal or wood or even as a dead rat – which might be tossed into a firebox or furnace to be disposed of.
The idea of ‘Explosive Coal’ wasn’t new. The idea originated from the US Civil War, when Confederate Captain Thomas Edgeworth Courtenay designed a piece of cast iron, with a cavity which could be packed with gun powder, that looked like a lump of coal. The Courtenay described them as ‘Coal Torpedoes’, their aim was to damage a steam ship’s boiler enough to cause a catastrophic secondary explosion. While several vessels may have been damaged or sunk by these Coal Torpedoes, the claims are difficult to confirm.
It seems the idea of a coal bomb was resurrected in 1940 and initially a ‘Coal Borer’ was developed and available for use in theatre by mid-1940. The borer could be used by agents to make holes in lumps of coal which could be filled by plastic explosive and a detonator. This was soon superseded by an Explosive Coal Kit which included moulded fake coal and paints to allow agents to match the colour of local coal. The kit included instructions on how to prepare and use the coal bomb.
Arthur Christie, a lab assistant at Station XII, is quoted at length in Des Turner’s book on Station XII. Christie remembered being asked to drill large holes in some coal:
“Another task was collecting the biggest lumps of coal that I could find in the storeroom and taking them to the lab. I had no idea what they wanted them for; it was seldom explained to me and, when it was, it was often as clear as mud. My instructions were to try to drill a large hole in each piece of coal without shattering it. I tried with a brace and a six-inch long tube that had a serrated end. I found that, if too much pressure was applied, the coal would disintegrate. I thought, I wonder what the hell they want this for? Don’t ask, just do it, and I did manage to drill three lumps of coal. I placed the drilled coal on the table of the MI room and set off for the officers’ dining room to inform the CO that I had been successful. I was told to insert about a quarter of a pound of PE and a detonator into the hole and glue the coal dust back over it. The mud in my brain now began to clear. The lump of coal could be placed in the coal tender of a locomotive and find its way into the firebox, or perhaps into the furnace of a factory. Later the PE was dyed black, which was better than using coal dust and glue. This idea led to plastic explosive being moulded into a multitude of objects and colours to fool the enemy.”
Frederic Boyce & David Everett, in their book SOE: The Scientific Secrets, credit Station XV with the development of a moulded clam-shell design using dyed Herculite plaster and coated with real coal dust. A photograph of this can be seen in the SOE’s Descriptive Catalogue of Special Devices and Supplies, along with ‘Explosive Wood’, or as it was officially known ‘Wooden Logs, Explosive’.
Eventually this was replaced by a bomb based around a charge in a metal casing that allowed liquid plaster to be poured around it, simplifying production and removing any sign of a seam. The coal bombs were detonated by a No.27 Detonator to which either a match headed safety fuse or a time delay fuse was attached.
Once the danger of coal bombs was discovered by the enemy it was also believed that they would have considerable a psychological impact and also cause the enemy to expend considerable resources on protecting and checking coal supplies.
The ‘Explosive Coal’ we see in the footage appears to actually be an incendiary bomb, producing a large amount of flame and heat. This would have been ineffective in a boiler but with a time delay or other sort of fuse it may have been very effective in causing a coal bunker fire aboard a ship, in a factory store, at a coal depot or in a locomotive’s coal tender. Coal fires are extremely difficult to contain and put out.
How effective Explosive Coal was is unclear but it is believed that coal bombs were used by both the SOE and their American counterparts the OSS. Boyce & Everett estimate that about 3.5 tons of explosive coal was made between 1941 and 1945. I’m unsure how many of these were explosive and how many were incendiary, like that seen in the footage here, but it’s a fascinating asymmetric method of targeting enemy infrastructure at the most basic level.
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Thanks to WW2Talk on twitter for their help getting me some scans from the SOE’s Descriptive Catalogue
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 4324 and is used under the Non-commercial Use agreement.
The Armourers Bench 
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