Flame Obstacles

A number of anti-tank Flame Weapons were developed by the during the War:

  • Flame Trap

  • Fougasse

  • Barrel Traps

  • Home Guard Flame Throwers


The Flame Trap was the most simple flame weapon and involved flooding a defile with a mixture of petrol and DERV (the recommended ratio was 25:75).  A road with a slope towards the enemy was preferable as the mixture would flow by gravity but the trap could be used on level roads with a pump. It required a good road surface which did not have a heavy camber.  The trap was lined with sandbags to prevent the mixture flowing into the drains and with a tank and hoses placed in position under cover. On the approach of the enemy the taps would be opened and the trap became flooded and was ignited electrically or with a Molotov Cocktail when the tank was in the trap.


Its main advantage was that the tank could not affect the trap with fire power. It was considered that once the method was in use, tanks could be bluffed by flooding the road with water.


The amount of fuel required was two gallons per square foot of road for one hours burning. The Petroleum Department made available to the Army a number of 500 gallon tankers which carried pumps (about 30 lorries per Command) in July 1940. However the idea was not really taken up as the trap had a number of problems:

  • It required a great quantity of fuel (for a 100 ft length of road by 15 ft wide, no less than 3,000 gallons were required).

  • It required the tank to be halted (e.g. to demolish a road block) as the time taken to ignite the trap precluded any chance of catching a moving tank.

  • It would require a site where a tanker could be adequately hidden and camouflaged.


Given the above, it was considered the only suitable location for a trap would be in a deep cutting with enough of a curve to hide a tanker and with a road block to stop a tank or in built up areas which would mean sacrificing houses.


Only three Flame Traps were constructed in Suffolk during 1940.


Both the Flame Fougasse and Barrel Trap avoided the problems of delayed ignition of the Flame Trap by projecting burning liquid at an approaching enemy.  Both were still best employed at locations where the enemy was forced to slow or stop, although they could be installed with a trip device so that the enemy vehicle would fire the device automatically.


Although it could be used against troops and AFV’s it was considered most effective against AFV’s by:

  • Destroying rubber tyres and exposed transmission gear

  • Blocking observation loopholes

  • Blinding the periscope

  • Getting into all crannies of a vehicle, creating a furnace that would make it untenable for its crew

  • Bursting over the louvers, being drawn into the vehicle itself and asphyxiating the crew.


Flame Fougasse


These were standard 40 gallon oil drums filled with 25% petrol and 75% oil. A firing and propelling charge would be fired simultaneously from a standard commercial wireless high tension 100-200 volt battery.  A beam of burning oil about 10 ft wide was projected to a range of about 30 yards.  The most effective range was when the target was within 10 yards of the trap; any further away then less than half the oil would strike the target (as the burning oil was consumed the farther it travelled). They could be installed as follows:

  • Emplacements excavated in a bank at the side of a road

  • A mound of sand or earth at the side of the road

  • Specially constructed blocks forming part of the actual road block.


The barrels were usually employed in groups of four – a hit from a single barrel could immobilize a vehicle but the narrow beam from each barrel meant a greater chance of a hit if four barrels were fired together.  The barrels were buried in the bank obliquely, facing the enemy and with between one to four yards between each barrel.  A length of 4” drainpipe was buried behind each barrel so the charge could be inserted when required.  The greater the depth of earth and the tighter it was packed around the trap, then the better the trap worked, as more of the force of the charge was directed towards the end of the barrel.  A minimum of two ft of earth above the rap and four ft behind was recommended. As a barrel was two ft in diameter and 3 ft long, a minimum roadside bank would be four ft high and seven ft thick. However the range varied greatly due to the density and wetness of the soil.
















                            Above: Flame Fougasse



Barrel Trap


There were two types of Barrel Traps, each using standard 40 gallon drums.  It was recommended that they be employed at not less than four barrels at each site. They had the advantage that they could be set up quickly provided a charge was already made up.


Demigasse –  a charge was placed in a hole  about 8” deep and 6” wide and the barrel rolled over the charge with its rear strengthening rib lying over the charge. When fired a sheet of flame and burning oil about 36 yards square was produced, the barrel being projected about six yards.


Hedgehopper – consisted of a drum standing on end either on the side of a road or concealed behind a wall or hedge.  The charge was buried as for the Demigasse. The charge should not be closer than five ft to the wall/hedge it had to jump. When fired it jumped about 10 ft high and 10 yards horizontally and flooded the area it landed on with a sheet of flame.


















 Above: Left - Demigasse.   Middle and right - Hedgehopper


Fougasses and Barrel Traps were widely installed by Commands. By May 1941 Commands had made demands for 30,000 barrels (which would require 800 tons of steel), 14,000 batteries and two million yards of cable. In June 1941 instructions were issued that each Chemical Warfare Group should hold a supply of 600 barrels for installation after any invasion began, as required by the tactical situation. As no further barrels were to be issued, Commands had to find the barrels from their existing stock.  Eastern Command, which had one Chemical Warfare Group attached, had been issued with 6,000 barrels and so had to find 600 out this stock for the Chemical Warfare Group.


Home Guard Flame Throwers


These were similar to the static Flame Traps developed by the Petroleum Department, except that they were mobile and could be pulled or pushed by a team of five or six Home Guard.  They were cumbersome weapons and only mobile in the sense that they could be stored centrally and moved to a position under threat; they were still essentially to be employed for the defence of a selected strong point or road block.  Selected positions for the Flame Thrower should be prepared in advance.


The “Home Guard” Flame Thrower was a 50 to 65 gallon drum mounted on a car axle.   It used a fuel of 40% motor spirit and 60% diesel oil. A pump was supplied along with approx 90 ft of 1½” flexible delivery hose. A section of 1½” steel pipe was attached to the hose, which had the jet attached. Ignition was achieved by attaching a small tin can to the jet which would throw out one or more small spray jets into the can, which when lit remained alight and so kept the main jet alight.


















Above: The "Home Guard" Flame-Thrower


The Harvey Flamethrower consisted of a 22 gallon cylinder filled with creosote and was mounted on wheels.  A 25 ft flexible hose fitted with a nozzle was connected to the cylinder. It could throw a jet of flame to a range of 50 yards with a full cylinder, the range decreasing as the cylinder emptied. Harvey Flame Throwers were certainly issued to some Home Guard in Suffolk from 1941.





























             Above: The Harvey Flame-Thrower

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