Operation Pluto

(Not) Supplying D-Day with fuel

An American soldier working on a pipe of the Pluto pipeline
(Photo: National Archives)

The success of any military operation greatly depends on logistics. Not even the best-trained men can win if they don't have the food, the ammunition and the supplies where they need it, when they need it – and fuel was added to that list as a major item in the era of modern industrial warfare.

Supplying fighting troops with fuel was going to be an especially tricky task on and after D-Day and the push across Normandy afterward, since land supply routes could not cross the English Channel. Operation Pluto, the name either standing for "Pipeline Under The Ocean" or "Pipeline Underwater Transportation of Oil" (sources contradict each other) was an attempt to solve the problem with what was cutting-edge engineering at the time. The practical usefulness of pumping fuel to France through submarine pipes has since been called into question, but the project remains a testament to the importance of engineering solutions in modern war.

The question of how to get fuel to the invasion troops was raised in April 1942, more than two years before D-Day. Vice-Admiral Lord Louis Mountbatten (Read our earlier article), the Chief of Combined Operations, doubted that a French port with oil-reception facilities could be captured by the initial landing force quickly enough to supply the invasion. He approached Geoffrey Lloyd, the minister in charge of the Petroleum Warfare Department, a department set up early in the war to develop gasoline-based flame and explosive weapons against a possible German invasion of Britain, asking whether gasoline could be pumped across the Channel in pipes. Examples of underwater pipelines transporting oil already existed, but not on anything resembling the scale that would be needed for the liberation of Normandy.

Geoffrey Lloyd, head of the Petroleum Warfare Department
(Image: British Pathé)

Due to the unprecedented scope of the undertaking, laying such pipelines (the “Major System”) was only going to be a backup solution. Shallow-draft coastal tankers, which could approach the shore, and larger tankers pumping fuel ashore through shorter pipes (code named "Tombola", known also as the “Minor System”), were going to be the solution of choice, along with twenty million jerrycans for the first days of the landing. The ships, however, also represented problems. The coastal waters of Normandy were going to be clogged with cargo and personnel transports bringing in a steady flow of supplies and reinforcements, and the tankers were only going to make the traffic worse. The frequent storms of the English Channel also threatened to impair such operations. And finally, large and slow oil tankers were going to be an irresistible target for whatever planes the Luftwaffe could get in the air. It was decided to work on a pipeline as safety option.

A T2 tanker, the type used in “Tombola” to pipe gasoline from ship to shore
(Photo: U.S. Navy)

The idea of how to make the pipeline work came from Clifford Hartley, Chief Engineer of the Anglo-Iranian Oil Company, who recollected how small-diameter pipes were used to transport 100,000 gallons of oil per day across the desert in Iran. A single long, flexible pipe could be laid across the Channel in a single night, hidden from the eyes of the Luftwaffe. The narrow bore could be compensated for by pushing the fuel across at high pressure. This would also have the advantage of allowing the same pipe to transport different types of fuels one after the other. At high pressure, different fuel types (such as aviation gasoline followed by diesel oil) would remain separated, while a low-pressure transfer would allow them to mix.

The structural inspiration from the pipe came from submarine telegraph cables, only with the insulation and the conductive metal core removed, since that's where the fuel would go. The prototype of the pipe had an internal diameter of 2 inches (5 cm). The pipe itself was made of extruded lead. That was surrounded by asphalt and cotton tape impregnated with vinylite resin. Over that was wound steel tape for added strength and flexibility, followed by jute tape and asphalt-impregnated paper. That, in turn, was wrapped in a layer composed of multiple galvanized steel wires that acted as armor, and finally, canvas.

A stripped-away section of Hais pipe, showing the layers
(Photo: Geni / Wikipedia)

The pipe was codenamed "Hais," an acronym of the designer's name (Hartley), the company he worked at (Anglo-Iranian), and the manufacturer of the pipe, Siemens Brothers and Company. A wider version of the pipe was also developed later, with the 3-inch (7.6 cm) internal diameter that could transport more than twice the amount of fuel at the same pressure. The pipe was tested and worked fine at a pressure of 1,500 psi (10,000 kPa) without problems, and could withstand more than twice that much pressure before destruction. A single continuous length of Hais pipe was 35 nautical miles (40 miles, 65 km) long and weighed 2,000 tons empty. It had to be filled with water so that the hollow structure would not collapse during handling, loading or laying, or from the pressure deep underwater. 570 nautical miles (817 miles, 1,310 km) of Hais cable were produced, 570 nautical miles in Britain and 140 nautical miles in the U.S. Multiple lengths could be connected together by mounting main body pieces at the ends and joining them with a split ring muff.

A 35-nautical-mile length of Hais cable being coiled up
(Photo: greenwichindustrialhistory.blogspot.com)

One drawback of the Hais pipe was its reliance on lead, which was in short supply; the Petroleum Warfare Department therefore also sought an alternative solution that didn't use the metal. Engineers Bernard J. Ellis and H. A. Hammick teamed up to design a pipe that eschewed lead. The "Hamel" pipe, its codename derived from a combination of Hammick and Ellis, was made from 40-foot (12 m) sections of mild steel. The sections were welded together with flash welding: the sections were placed very close to each other but not touching, and were then electrified. The air gap between the two metal objects caused an electric arc to form and heat up the ends next to each other to a point where they started to melt; the melting ends that touched and fused together. The 40-foot sections were thus welded together into 4,000-foot (1,200 m) segments. These segments could then be welded together into longer spans.

Loading the Hamel pipe aboard ships proved to be a problem. The Hais pipe was flexible enough that it could be coiled up and stored in the hold of a ship. From there, it could then be led through guides to the ship's stern and lowered into the water.

A Hais pipe being raised from the hold of a ship and led towards the stern for laying
(Photo: Imperial War Museums)

The Hamel, however, wasn't nearly that flexible, and coiling it up to the same size would have broken it due to the material stress. A special solution was needed – and found in the so-called Conundrum. The Conundrum was a massive hollow steel drum 60 ft (18 m) long and 40 ft (12 m) in diameter, ending in flat cones on both sides to make it easier to mount on a ship, and capable of being rotated by a sprocket chain attached to an electric motor. As the 4,000 ft long Hamel pipe segments were manufactured near the shore, they were conveyed to the drum, and one was reeled onto it. When it was almost completely on the drum, its end was welded to the next pipe segment, and the reeling continued. This process continued until the drum held 90 miles (145 km) of pipe. The width of the giant drum meant that the bend of the pipe was gentle enough and it didn't break. The six Conundrums used in the operation could be then attached behind a ship and towed across the Channel while the pipe was reeled off in reverse. Since the drums were used at sea, they were unofficially given the "HMS" designation reserved for Royal Navy vessels and named HMS Conundrum 1 to 6.

A Conundrum loaded with Hamel pipe, ready for laying
(Photo: Imperial War Museums)

Another important element of the pipeline system were the pumping stations located in England near the shore. The Luftwaffe bombing these facilities would have caused to entire operation to grind to a halt, so their construction was surrounded by great secrecy. No labels or correspondence related to them could bear the words "Petroleum Warfare Department" or its acronym. The locations appeared on no maps. Truck drivers bringing construction materials were only told the general area; they then had to call a certain number from a public phone to receive verbal instructions to the site.

A seemingly innocuous residential house hiding pumping equipment
(Photo: Imperial War Museums)

The buildings themselves were disguised as innocuous locations such as cottages, amusement parks and old forts. One particular facility was camouflaged as an ice cream parlor and serves as a mini-golf course today. Another was disguised as a large pile of gravel right next to an already existing real quarry.

A pump house disguised as a mound of gravel
(Photo: Imperial War Museums)

While the real facilities were carefully hidden, a fake oil dock was constructed in plain sight at Dover, where the English Channel was the narrowest, to suggest that the upcoming invasion was going to depart from there and target the French city of Calais. The three-acre dock contained fake pipelines, storage tanks, vehicle parks and anti-aircraft emplacements, was guarded by military police, and used wind machines to create a dust cloud to simulate activity. King George VI, General Eisenhower and British General Montgomery all visited the fake dock to make the deception more believable.

4,000-foot sections of Hamel pipe awaiting assembly and loading onto a Conundrum
(Photo: Imperial War Museums)

The first underwater pipeline was to be laid from the Isle of Wight in Southern England to the French port of Cherbourg (Read our earlier article), which was supposed to be liberated eight days after D-Day (D+8), with the pipeline fully entering service on D+75. Since "Pluto" already suggested a Disney-related theme (Read our earlier article), the pipeline was named Bambi. Due to the presence of unexpected German forces and their tough resistance, however, the port of Cherbourg was only captured on June 27 (D+21), and was so heavily demolished and booby-trapped by the Germans that it took even longer to repair and set into service. Coastal tankers and Tombola pipelines had to pick up the slack and supply the freshly landed invasion forces with fuel.

The first Hais pipe, over 60 miles (96 km) long, was laid down between the Isle of Wight and Cherbourg on August 12 in 10 hours. It promptly failed when the lowered anchor of one of the escorting destroyers snagged on the pipe and damaged it beyond repair. The second attempt failed two days later when the pipe fouled (got entangled) on the propeller of a supporting ship. A Hamel pipe failed less than two weeks later because ten tons of barnacles attached themselves to the submerged part of the Conundrum and the extra mass rendered it incapable of rotating. The barnacles were scraped off and another made a few days later, but the steel pipe broke 29 nautical miles (33 mi, 54 km) out. Finally, a Hais and a Hamel pipe were laid down successfully in late September, but both failed on October 3 when the pressure was increased to pump across more fuel. Bambi was shut down the next day, after only receiving 3,700 U.S. tons of fuel.

A Conundrum laying down Hamel pipe to Cherbourg
(Photo: Imperial War Museums)

A second set of pipes, code named Dumbo, began to be laid down further east between Dungeness and Boulogne, across the Strait of Dover, where the channel was only 23 nautical miles (26 mi, 43 km) across. The work commenced in late October, and 6 Hais and 11 Hamel pipes were laid by December, pumping 1,460 U.S. tons of fuel each day. The Hais pipes proved very resilient, and the Hamels needed repairs every 68 days on average. The pipes had to be run at lower pressures than originally planned, so the original plans of pumping multiple fuel types through the same pipe had to be scrapped and Dumbo only transported gasoline.

Pluto pipes beside the road in Normandy
(Photo: National Archives)

The major Belgian port of Antwerp had been liberated by December, and, combined with other ports, could handle a much higher volume of fuel than the pipes. Abandoning Operation Pluto was considered, but ultimately rejected because Antwerp was still under regular German attacks by V-1 flying bombs (Read our earlier article) and V-2 rockets, and only Antwerp and Cherbourg could receive large tankers. Additionally, keeping Dumbo running also meant that some of the coastal tankers used to supply troops in Europe could be released for service in the Far East. Dumbo not only continued to operate, but was greatly expanded inland as Allied troops pushed on eastward toward Germany. By the end of the war, the inland part of Dumbo extended through Antwerp and the Dutch city of Eindhoven, all the way to the German city of Emmerich that stands on the Rhine. By April 3, 1945, Dumbo was carrying 5,040 U.S. tons of gasoline to troops deep in Europe.

Pluto pipes heading toward reservoir tanks
(Photo: U.S. Army Signal Corps)

How important was Operation Pluto to the Allied war effort? While originally intended as a backup solution, some historians credit it with being a great help to the troops making their way through Europe. Others point out that the amount of gasoline sent to the continent via the pipelines was dwarfed by the amount transported by tankers, that Bambi failed to be of use during the critical early stages of the invasion, and that Dumbo came online only once the need for fuel was no longer so pressing. But whatever Pluto's strictly military utility might be, there's no doubt that it was an outstanding engineering accomplishment that paved the way for many similar peacetime future endeavors. As Prime Minister Winston Churchill noted, it was "a wholly British achievement and a piece of amphibious engineering skill of which we may well be proud."

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A monument dedicated to Operation Pluto in the French coastal town of Port-en-Bessin
(Photo: Author’s own)

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