"Flame all across Britain"

The Petroleum Warfare Department

Humanity, like much of the animal kingdom, has a deeply seated fear of fire; the sight of an inferno raging out of control can awaken an unrivaled primal terror in us. In 1940, a battered Britain, demoralized after the fall of France and fearful of the prospect of a German invasion (Read our earlier article), reached for this ancestral fear for defense. The task of the Petroleum Warfare Department was to use fire as a defense against invasion. One of the architects of the plan, Secretary of Petroleum Geoffrey Lloyd, shared his vision thus: "Flame all across Britain ringing the coasts, spurting from the hedges and rolling down the hills. We will burn the invader back into the sea." 

The British military was in dire straits after the Dunkirk evacuation (Read our earlier article): the Army, the Navy and the Air Force had to be rapidly expanded, equipment lost in the evacuation replaced, and volunteer organizations like the Home Guard had to be integrated into the nation's defense. Many types of material and equipment were suddenly in short supply.

One thing Britain had plenty of was oil: even though import from the Middle East stopped, American shipments provided the country with plenty, at least for the time being. (In fact, gas rationing was originally introduced and motoring for pleasure discouraged not due to shortages, but to prevent tight clusters of fueled-up cars providing a tempting target for German bombers.)

The presence of fuel was, in fact, even considered a problem in the south of England, since a German invasion force might have been able to capture and use those stores. Gas stations near the coast were either emptied or had their pumps disabled, while others were required to draw up plans to prevent the invaders from getting their gas.

However, a new idea was raised even as the Dunkirk evacuation was still going on: instead of just keeping the gasoline safe from the Germans, why not use some of it as a cheap and available weapon against an invasion? On May 29, 1940, former public servant Maurice Hankey, then serving as a cabinet minister without portfolio, was brought on to the Ministerial Committee on Civil Defence. Back in World War I, it was Hankey who took notice of the ideas of one Major Ernest Swinton about an armed, tracked vehicle that could cross no man's land and enemy trenches, and brought them to the attention of then-First Lord of the Admiralty Winston Churchill, indirectly prodding the development of the tank. Hankey also took interest in using fire weapons such as flamethrowers in a defensive role. In 1940, he brought up those ideas again, and Churchill, always interested in new technologies, authorized the Secretary of Petroleum to begin experiments on June 5 with Hankey as supervisor.

Another key figure was Major-General Sir Donald Banks, who served as the Director-General of the newly established Petroleum Warfare Department. While fighting in France during the German invasion, he once saw a burning ship from a clifftop: "A few miles away an oil tanker had been bombed or had struck a mine. Masses of the blackest smoke pillared up into a gigantic pall in the sky while in the vast lake of fire, spreading it seemed for miles on the water a flame blazed and leapt like an angry volcano [...] I was often to recall that scene in subsequent days of Flame Warfare." Banks approached the work of the department with a mixture of enthusiasm and skepticism over the viability of a large, centralized effort to develop such weapons. The department began work on July 9, 1940, operating in three small rooms with a tiny staff that completely lacked technical knowledge.

The Dunkirk evacuation not only prompted the creation of the department, but also provided an early inspiration. During the retreat, British troops once built a makeshift barricade from vehicles and furniture, with several punctured gas tanks hidden underneath. Once a German tank started climbing up the barricade, the gas was ignited, forcing the tank to rapidly back off. Experiments inspired by the event led to the department's first practical weapon: the static flame trap.

The trap could be built along a 60-150 ft (18-46 m) stretch of road, often a sunken road which vehicles couldn't leave.  Perforated pipes were placed alongside the road, sometimes hidden in a gutter or disguised as handrails. The pipes were connected to a large tank located nearby on higher ground and away from sight, filled with a mixture of 25% gasoline and 75% gas-oil (a type of fuel oil). A Home Guardsman could simply turn a valve to cause the mixture to flow down the pipes and onto the road, then light it with a Molotov cocktail or a flare gun. The resulting conflagration would engulf men and vehicles on the road, and one public demonstration proved so hot that it burned off the road surface. Later improvements removed the need for manual ignition: once the gas started flowing and reached the end of the pipe, its pressure would cause two chemicals to mix and start a spontaneous combustion. The system was not only effective, but also cheap, as it required pipes that were commercially available, and could be installed by employees from oil companies. Some 200 such traps were built, along with a number of mobile traps where the fuel was carried in tanks or drums atop trucks.

Another weapon was designed by two World War I experts of fire warfare. Henry Newton developed a medium mortar during the war; William Howard Livens was the inventor of a variety of weapons, including a giant flamethrower and a cheaply produced "projector," a simplistic launcher that could hurl drums of inflammable or toxic chemicals. At the Petroleum Warfare Department, they started by experimenting with a version of the Livens projector that could use commercially available 5-gallon drums, and with a device that would shoot milk bottles filled with phosphorus from a rifle. Neither of these ideas panned out, but they led to something far better: the flame fougasse.

The flame fougasse was inspired by and named after the fougasse, a weapon that already existed in the late Middle Ages and also saw use in the American Revolutionary War and the Civil War. The original fougasse was a drum-shaped hole in the ground or in solid rock, filled with gunpowder and projectiles like rocks or mortar shells. Once the powder was lit, its explosion propelled the contents of the hole at the enemy.

The flame fougasse was similar, only it used an actual barrel instead of a hole, and it launched a plume of burning fuel instead of solid objects. It came in three versions.

The "safety fougasse" was a drum dug into a roadside slope or embankment in a horizontal position, with one end pointing at the road and lightly camouflaged. From the top of the embankment, a stove or drainpipe was dug into the ground straight down so it terminated at the back end of the barrel and topped with a cap to keep water out. It was a "safety" fougasse because the electrically detonated propelling charge could be kept elsewhere and lowered to the back of the drum down the pipe when its use was imminent – this prevented both accidental discharges and the propelling charge turning inoperable from humidity.

The "demigasse" was even simpler. Instead of hiding the barrel, it was simply left lying on its side by the road on its side, with a charge hidden in a small hole under it. Once the charge was detonated, it both ruptured the barrel and flipped it over, with the flipping motion spraying burning fuel out of the rupture. These standard 44 imperial gallon (53 US gallon; 200 liter) barrels were indistinguishable from those used to hold tar near road construction areas. It was hoped that after the first few incidents, the German invaders would grow paranoid and stop to blast every drum, even ordinary tar ones, before moving on.

The third, fanciest version of the flame fougasse was the "hedge hopper." This was standing up with a charge underneath it, hidden behind a hedge or wall no taller than 10 ft (3 m). Once detonated, the charge launched the barrel into the air, over the hedge and onto the road. (At least in theory, since it was rather hard to aim.)

50,000 flame fougasse barrels were made, with most of them deployed during the war in batteries ranging from a single barrel at a site to fourteen, with batteries of four being the most common. The drums used two different types of fuel: one was 40% gasoline and 60% gas-oil (a mixture unsuited for vehicles), and the other, named "5B," was a dark, sticky paste of tar, lime and petrol gel that stuck to whatever it hit while burning. Flame fougasses have seen use in later conflicts including the Korean and Vietnam Wars, and remain in army field manuals as easily constructed traps.

Of course, stopping the Germans with fire while they're still on the way would have been even better than stopping them once they've landed, so the department also experimented with water-based fire weapons. A ship could pour oil on the water behind it, creating a floating wall of flame. In order to prevent the oil slicks from breaking up, the ship had a device on deck that turned coconut fiber into a floating trough and lowered it into the water to trap the oil. At a demonstration, the ship produced a flaming ribbon 880 yards (804 m) long, 6 ft (2 m) wide and towed at 4 knots, but the plan didn't go ahead.

A more ambitious idea took a clue from the historical fire ships that had been in use since ancient times: take three old, barely seaworthy oil tankers, fill them with oil and whatever explosives were at hand, and sail them to Boulogne, where the Germans were hoarding barges for the upcoming invasion. Once a few miles away from the port's mouth, most crewmen would disembark, except for three, who would set detonation timers and escape in motorboats at the last minute. Once the ships exploded, the rising tide would draw the giant slicks of burning oil into the harbor and burn the barges.

The plan appealed to Churchill, since it mirrored how Sir Francis Drake attacked the Spanish Armada in 1588, and he gave Operation Lucid the go-ahead. Four attempts were made in the fall of 1940. The first was called off after two of the three tankers pulled out, once due to unfavorable winds and the other due to boiler troubles. The second and third tries were foiled by bad weather. The fourth attempt was canceled when an escorting destroyer hit an acoustic mine and the fleet had to disperse to avoid any others that might have been nearby. The operation was postponed until the spring of 1941, but the threat of a German invasion had dissipated by then.

A more grandiose idea was to set the sea itself on fire. Several experiments were conducted with the goal of spreading oil into the sea via a set of pipes, and setting it on fire to create massive walls of flames. 50 miles (80 km) of such coastal flame barrages were approved in early 1941, but only a fraction of that was ever built. On more careful consideration, the idea proved to be expensive and difficult to implement, and the walls of fire were short-lived and actually provided approaching vessels with a smoke cover.

The department also developed more traditional flame weapons, such as several semi-portable flamethrowers whose tanks could be carted along on wheels, which ended up with the Home Guard. The Cockatrice was an armored truck with a flamethrower on top and came in light and heavy versions. The defense of coastal bases against German paratrooper landings was a concern. The British knew that German Fallschirmjäger jumped only with their pistols, with bigger weapons dropped in separate pods, which forced them to spend some time arming themselves and assembling. The Cockatrices, sixty of which were made, were stationed at such bases and were supposed to rapidly drive out to the landing zone and burn the Germans before they could get battle-ready.

The same flamethrowers were also mounted on some small ships to discourage German air attacks. German pilots liked to come in very low to avoid detection, and dropping their bombs before flying over ships just above mast-height. While the flamethrower had a normal range of about 100 yards (91 m), this increased to three times as much when firing directly upward due to the hot up-draft. Dummy attacks by test pilots proved disheartening, but that was because one pilot was briefed in advance on what to expect, and another had worked as a stuntman and was used to driving cars through fire. The few vessels armed with the weapon failed to down any German planes, but it was observed that German pilots increased the altitude of their attacks. 

The department's flamethrowers were also mounted on more traditional vehicles: flamethrower tanks were put to good use later, on D-Day, with Hobart's Funnies (Read our earlier article). "Ronson" type flamethrowers were also mounted on the ubiquitous Universal Carrier, which were named Wasps in this configuration.

Operation Pluto, short for "Pipeline Under The Ocean," was also carried out with the help of the Petroleum Warfare Department, and you can read our separate article about it here.

Another nonviolent development by the department was FIDO, short for Fog Investigation and Dispersal Operation. British fog was a major hazard to planes trying to land, especially for warplanes that might be low on fuel, flown by a wounded pilot, or have suffered combat damage. On the night of 16-17 October 1940, a force of 73 bombers lost 3 planes to enemy fire but 10 to crashlanding, caused Churchill to order the development of a solution.

Prewar studies showed that fog evaporates if its temperature rises by about 5°F (3°C). The department developed something a bit like the static flame trap, only larger, with the pipes running along runways and shooting fire to heat up and evaporate some of the fog (and to outline the landing spot at night). The first version used a mixture of gasoline and alcohol, but it replaced the fog with smoke. A solution was found by preheating the gasoline: the pipes were laid down in such a way that the pipe carrying the fuel ran adjacent to the evaporator pipe shooting fire. The heat of the fire caused the fuel in the other pipe to heat up and become vaporous, which made it burn without smoke. It's hard to say how effective the system was, but one estimate claims that some 3,500 lives were saved by the system, and another 10,000 were helped by making a serious landing situation at least somewhat easier. The FIDO system was also installed at some American airfields, and was considered for commercial use after the war, but development in landing technology rapidly made it redundant.

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