Although no longer in service, the construction of the PLUTO Pipeline was an amazing feat, involving the collaboration of rival commercial firms, government departments and the armed services, to construct a subsea pipeline, which would deliver more than one million gallons of petrol per day across the English Channel during World War II.

Petrol supplies were integral to successful war operations for the troops, and were initially being supplied via four gallon tins in jerricans carried across the beaches. A bulk supply of fuel was necessary and delivery by tanker was then trialled, but hazards such as weather and attack threatened the interruption of supply. It was decided that a pipeline across the Channel was the best form of transportation to ensure a reliable supply of petrol.

Conventional construction methods at the depth required would mean that heavy moorings and large craft would be needed, and weather conditions would make construction hazardous. In addition, the time taken to join pipe on a pipelay barge would render enemy interference by sea and air very easy. As such, two new types of oil pipeline were manufactured:

• The Hartley Anglo-Iranian Siemens (Hais) pipe
• The Hammick Ellis (Hamel) steel pipe.

In order to ensure success, it was suggested that the pipe be made in one complete length so that no stopping would be required when laying the pipe. This required the use of small diameter pipe due to issues of bulk and weight, and a very high working pressure would ensure that a larger amount of petrol would be transported through the pipe.

The Hais pipe

In 1942, the Anglo-Iranian Oil Co, Siemens Brothers and Co, and (later) rival company Henleys, were enlisted to make a test pipe armoured with steel tape and wire, and a lead covering.

Test lengths were laid in deep water off the Clyde, under both severe and easy conditions. Following these tests, six 30 mile long operational lengths of 2 inch diameter were manufactured for a full-scale trial in the Bristol Channel where conditions of tide and depth of water were more severe than those in the English Channel.

Special cable ships were equipped to carry a sufficient length of the pipe. The SS London, a 1,500 tonne coaster, was made available and renamed HMS Holdfast.

A pumping station was erected on the sea wall at Queen’s Dock, Bristol, that connected to the Royal Army Service Corps’ Bulk Petroleum Co’s petrol tanks, and a receiving terminal was constructed in Watermouth Bay, near Ilfracombe.

During testing, a German raid on Swansea proved that the pipe would not be damaged by a bomb within 100 feet and, during a gale, a ship at the Mumbles anchorage dragged the pipe with her anchor. HMS Holdfast had no difficulty in locating the pipe, cutting out the damaged portion, and running in a new length.

After further testing, it was found that 3 inch pipe could be produced using existing facilities and that it would deliver 2 ¾ times more petrol than the previously-manufactured 2 inch pipe.

The pipe was encased in a lead sheath, manufactured in 700 yard lengths. The sheath was coated in a layer of petroleum residue compound, followed by two layers of compounded paper tape. The wrapping was then followed by one layer of compounded cotton tape to give a bedding for the steel tape and also to increase flexibility. Then, four layers of steel tape were applied.

The finished pipe weighed 63 tonnes per nautical mile. The line was made in continuous lengths of 35 nautical miles, coiled direct from the armouring machine into special storage sites to await loading on the ship.

Pipe joints were made petrol-tight with petrol-resisting rubber-moulded rings against the lead pipe while at the same time preventing the lead from being distorted or extruded.

The Hamel pipe

The second novel proposal came at the end of April 1942. When dealing with the Hais pipe it became apparent that the pipe was flexible in a long length, although extremely stiff in a short length. Steel pipe, also flexible in long lengths, was suggested for making long lengths of line required in one piece.

Preliminary work proved that the steel pipe could be bent and pulled off straight, that it could be welded with absolute reliability, and that it could be carried and laid by either the wheel and barge but there was no previous experience as to how bare steel pipe would behave on the bottom of the sea.

It was expected that the 3.5 inch diameter low carbon mild steel pipe would have a lifespan of at least six weeks, allowing the delivery of sufficient supplies. Standard 40 foot lengths of pipe were welded to form lengths of 4,000 feet. The pipeline had a wall thickness of 0.212 inches and a weight of 20.21 tonnes per nautical mile.

By April 1943, both the Hais and Hamel pipe had been brought successfully through full-scale trials.

A new tactic

During June and July 1943, it was decided that the English pipeline system should be extended to both Dungeness and to the Isle of Wight and that pumping stations of 3,500 and 3,000 tonnes per day capacity, respectively, should be constructed at these places.

The Isle of Wight to Cherbourg Crossing involved a sea crossing of about 70 nautical miles instead of the 20 or so originally visualised, and made necessary the provision of larger cable ships and loaded down till the axles were awash. Following a successful lay with 3 inch Hais pipe, three more ships were converted and fitted with cable gear. Six Thames barges were equipped to handle the shore ends and a large number of auxiliary vessels were added to the force, whose personnel numbered 100 officers and 1,000 men.

The Petroleum Board constructed the land lines and SNO Pluto laid a large number of Hais and Hamel lines across the Solent (the strait separating the Isle of Wight from mainland England).

Construction

Construction of Operation PLUTO began on 12 August 1944. Two Hais pipes and two Hamel pipes were laid during the following weeks.

Petrol was pumped across to Cherbourg, but the Allied Armies’ rapid advance along the French Coast made it necessary to concentrate all efforts on the Dungeness crossing, and the Cherbourg lines were shut down.

The Dungeness lines were run to a beach inside the outer harbour of Boulogne, in order to save the time required to clear the heavily mined beach at Ambleteuse, which had previously been chosen. This involved a longer run and a more difficult approach, but the first was laid in October 1944 and after the technique had been perfected for laying the main lengths of Hais pipe, further lines were laid and commissioned with certainty and without incident.

Force Pluto was responsible for laying the line to above low water on each shore, after which the home end was connected with steel pipe to the valves and filters provided on the pump delivery lines, and at the far end to a valve manifold.

Eventually 11 Hais and six Hais-Hamel lines were laid with a capacity of more than 4,500 tonnes, or 1,350,000 gallons a day; and, 1 million gallons a day were pumped across for many weeks.

Success

No Hais pipe that had been satisfactorily laid and commissioned failed. The Hamel pipes on the other hand, while more than fulfilling the original estimate of six weeks of useful life, did fail successively in 77, 52, 55, 112, 55, and 60 days. The loss of petrol between tanks at Dungeness and at Boulogne was, however, less than 1.1 per cent for the whole operation.

The Supreme Allied Commander, General Eisenhower, described Pluto in his report as “second in daring only to the artificial harbours projects”, and wrote, “This provided our main supplies of fuel during the winter and spring campaigns.”