PLUTO (Pipeline Under the Ocean)

 2024 marks the 80th anniversary of Allied Invasion of Normandy in Operation Overlord, the largest seaborne invasion, codenamed Operation Neptune, often referred to as D-Day, 6th June.  Notable the day is best known as the Longest Day. 

Prior to the amphibious landings on the 6th, this was preceded by an extensive aerial and naval bombardment.  shortly after midnight, an airborne assault of 24,000 American, British and Canadian airborne troops landed.  Later that morning, 6.30, on a 50 mile stretch of the Normandy coast, troops landed on one of five sectors, named Utah, Omaha, Gold, Juno and Sword.    

During the first day, the Allies failed to achieve their goals.  Carentan, Saint-Lo and Bayeux were remained in German hands.  Caen wasn’t captured until the 21st July.

The need for petrol, oil and lubricants to support Operation Overlord, would have accounted for 60% of the supplies that was needed by expeditionary forces.  Pipelines would reduce the need for coastal tankers, these in turn could have been hindered by bad weather or they could have been subject to attack.

PLUTO (Pipeline Under the Ocean)

A new kind of pipeline was needed which could rapidly deployed.  Two pipeline systems were laid and each of them were camouflaged pumping stations to the Avonmouth-Thames Pipeline.  These pipelines were to be known as the PLUTO (Pipeline Under the Ocean). 

PLUTO (Pipeline Under the Ocean) Map

The first pipe from Sandown, Isle of Wight to Cherbourg was not very successful, becoming operational on the 22nd September, terminated on 4th October.  The second pipe from Dungeness, Kent to Boulogne began pumping on 26th October and expanded to 17 pipes by that December.  Was operational until 7th August 1945. 

However, prior to the pipes being laid and used, they must be developed.  Clifford Hartley, Chief Engineer of the Anglo-Iranian Oil Company, heard the proposal of pipeline after visiting Petroleum Warfare Department.  He pitched his proposal for a continuous length of pipeline like a submarine communication cable, but without the core and insulation to be deployed by a cable lying ship.  At high pressure the line could carry different types of fuel and at low pressure they could be mixed.

Sir William Fraser, Chairman of Anglo-Iranian Oil Company supported Hartley’s proposal.  Fraser was also petroleum advisor to the War Office.  There was further support from Siemens Brothers. 

Siemens Brothers developed the cable in conjunction with National Physical Laboratory, based on their existing undersea telegraph cable. 


The pipes were 2-inch diameter inner pipe, this was surrounded by a layer of asphalt and paper impregnated with vinylite resin. Steel tapes were wound around this to give it strength and flexibility.  Around this was a layer of jute tape and asphalt-impregnated paper.  Finally, it was covered by a protected layer of fifty galvanised steel wires.

Swansea - Ilfracombe via the Bristol Channel - 27 miles
Google Maps

HMS Holdfast
A trial took place during December 1942 using a prototype pipeline.  The pipeline went from the Queens Docks, Swansea  via the Bristol Channel to Watermouth Bay near Ilfracombe, North Devon.  The distance was 27 miles.  The pipe was laid by HMS Holdfast under the command of Commander Henry Treby-Heale.  The HMS Holdfast travelled only 5 knots during rough weather.  Further tests were carried on the sturdiness of the cable when two German 500 lbs bombs were dropped.  Later a ship’s anchor dragged the cable.  HMS Holdfast was able to locate and repair the damage. 

During the 3-week trial, the 2-inch cable was able to deliver 125 tons or 38,000 gallons a day.

When the pipe wasn’t needed what became of it?  Is it still there lying between Swansea and Ilfracombe?

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