Towed “Conundrums” spooled off steel pipe across the English Channel soon after D-Day.


To provide vital oil across the English Channel after the June 6, 1944, D-Day landings, secret pipelines were unwound from massive spools to reach French ports.  

Wartime planners knew that following the D-Day invasion Allied forces would need vast quantities of petroleum to continue the advance into Europe.

Rare logo of Operation Pluto secret pipelines during World War II.

The secret pipeline mission used a popular Walt Disney character for its logo.

Allied leadership also knew that petroleum tankers trying to reach French ports would be vulnerable to Luftwaffe attacks. A secret plan looked to using new undersea pipeline technologies.

To prevent fuel shortages from stalling the Normandy invasion, a top-secret “Operation PLUTO” – Pipe Line Under The Ocean – became the Allied strategy. It would fuel victory with oil production from the U.S. petroleum industry.

Although by 1942 the industry had laid thousands of pipe miles across all manner of terrain, to span the English Channel would require an unprecedented leap in technology. The channel was deep, the French ports distant, and the hazards unpredictable. In great secrecy, two approaches were developed.

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The first PLUTO system required a new kind of pipe that looked more like an undersea communications cable than an oil pipeline. It exploited existing subsea cable technology, but instead of a bundle of wiring at its core, a three-inch flexible lead pipe would carry fuel.

Operation Pluto pipeline map of English Channel.

Following D-Day on June 6, 1944, Operation Pluto pipelines fueled the advance into Nazi Germany. Image from “World War 2 From Space,” a History Channel documentary.

Each mile of this new pipe would use over 46 tons of lead, steel tape and armored wire – crossing almost 70 miles from Isle of Wight to Cherbourg.

Several unique ships would be needed to lay this new pipe under the channel. No existing communications cable laying ship could do it. A civilian passenger vessel, London, was the first to be modified to accommodate a huge spool around which the new pipe would be coiled. The first pipeline from Isle of Wight to Cherbourg was laid on August 14, 1944, with another to follow.

Enormous floating “conundrums" for oil pipelines.

Pipeline was wound onto enormous floating “conundrums” that were designed to spool off the pipe when towed. As the spools unwound, the pipe settled to the bottom of the English Channel.

An alternative approach proved even more successful. This method used three-inch steel pipe, which had proven to be flexible and durable in the oilfields of Iraq and Burma. The steel pipe could be wrapped around giant drums.

Secret Pipelines on a Spool

Welders assembled 20-foot sections of pipe into 4,000-foot lengths. The pipeline was wound onto enormous floating “conundrums” that were designed to spool off the pipe when towed.

Secret World War II pipeline being laid in English Channel.

Gen. Dwight Eisenhower declared Operation PLUTO, “Second in daring only to the artificial ‘Mulberry’ harbors”

These deployment systems weighed 1,600 tons each, and were pulled by three tugboats from the British site at Dungeness to the French port of Boulogne, 31 miles away. As the spools unwound, the pipe settled to the bottom of the English Channel.

Ultimately, using both methods, 17 pipelines supplied thousands gallons of fuel to Boulogne. By March 1945, one million gallons of fuel were being delivered each day and Allied success was assured. 

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Earlier in the war effort, the longest petroleum pipeline construction project ever undertaken had been completed in the United States – two pipelines spanning 1,200 miles. Learn more about them in Big Inch Pipelines of WW II.

 Modern pipelinelaying vessel at sea..

Modern pipelaying vessels can lay more than 3,800 tons of 16-inch pipe.

The end of World War II brought a hiatus to development of undersea pipeline technology. In the shallow Gulf of Mexico, the petroleum industry continued laying pipe by welding individual lengths of oil and gas pipe together aboard barges. The process required frequent halts for new sections to be added.

But by the 1960s, the World War II engineering feat of reel-laying began to reappear in the offshore industry. Operation PLUTO precedents can be seen in modern pipe-laying vessels unrolling coiled pipe to remarkable lengths. Vessels can lay more than 3,800 tons of pipe of up to 16 inches in diameter at a speed of more than 13 knots.

The massive, towed drums have receded into history. Coiled pipe reels now ride aboard specialized vessels — constructing a subsea infrastructure that safely connects oil and natural gas production platforms with refineries on shore.

Mulberrys: D-Day Jack-Up Rigs

“Second in daring only to the Mulberry Harbours, was PLUTO.” – Gen. Dwight D. Eisenhower.

The D-Day logistics of supplying troops put ashore on Omaha and Gold beaches in June 1944 included highly classified construction of artificial harbors, codenamed Mulberrys – employing the ancestors of today’s jack-up rigs.

Mulberrys used barges 200 feet long and 60 feet wide – each with four retractable 60-foot pylons to provide platforms to support floating causeways that extended to the beaches. Tons of supplies and equipment came ashore in the massive effort. Offshore drilling companies adopted this jack-up pier technology after the war.

Massive jack-up oil rig being towed beneath San Francisco bridge on Dec. 15, 1958.

San Francisco, December 15, 1958: “Seemingly towering above the Golden Gate Bridge, this ungainly barge with towering legs proceeds on its way towards the open sea. The towers, which will eventually serve as legs reaching to the ocean floor, were raised again after passing the bridge.”

Offshore exploration advanced rapidly after Kerr McGee’s 1947 success with the first producing well out of sight of land, the KerrMac No. 16, which stood in only 20 feet of water in the Gulf of Mexico. Surplus World War II tenders supplied these drilling operations.

Within ten years, in addition to tender-serviced platforms in shallow waters, jack-up rigs equipped with much larger pylons were operating successfully to depths of more than 150 feet.

Pylons grew in length from the original 60 feet to almost 300 feet. Col. Leon B. DeLong of the U.S. Army Corps of Engineers continued developing D-Day’s jack-up rig concept and after the war. DeLong designed platforms that began operating as Modular Offshore Drilling Units (MODU) miles from shore (see Offshore Oil History).

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Learn about another top-secret World War II “English Project” in Roughnecks of Sherwood Forest.


Recommended ReadingCode Name MULBERRY: The Planning Building and Operation of the Normandy Harbours (1977). Your Amazon purchase benefits the American Oil & Gas Historical Society. As an Amazon Associate, AOGHS earns a commission from qualifying purchases.


The American Oil & Gas Historical Society (AOGHS) preserves U.S. petroleum history. Become an AOGHS annual supporting member and help maintain this energy education website and expand historical research. For more information, contact © 2023 Bruce A. Wells.

Citation Information – Article Title: “PLUTO, Secret Pipelines of WW II.” Authors: B.A. Wells and K.L. Wells. Website Name: American Oil & Gas Historical Society. URL: Last Updated: June 3, 2023. Original Published Date: February 3, 2010.


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