Special duties: A flotilla od ships was enlisted to lay pipelines
The D-Day landings, commemorated last month, did not occur in isolation but were part of a wider plan. Pipe Line Under the Ocean, or Pluto, was a key project during the D-Day period. The aim was to lay petrol pipelines across the English Channel to supply the Allies.
Pipelines had proved essential earlier in the Second World War for delivering the vast amounts of petrol required for the mechanised armies in Egypt and North Africa.
Admiral Lord Louis Mountbatten, when Chief of Combined Operations, saw the urgent need for bulk supplies. He was developing means for pulling out short pipelines from beaches to a sufficient depth of water to allow small coastal tankers to discharge into tanks that were to be fixed on or near sand dunes. Following tests at Westward Ho! in Devon in 1942, this method was thought too risky of interruption by weather and enemy attack.
Geoffrey Lloyd, Secretary for Petroleum, was asked if English pipes could be extended to join up with continental lines to be laid by the Royal Engineers. His advisers were cautious. Even in peacetime, weather conditions could make it a hazardous operation. In wartime, the need to stop to make joints, use large flotillas and heavy moorings would render all known methods impossible.
On 15 April 1942 Arthur Hartley, chief engineer with Anglo-Iranian Oil, visited the government’s Petroleum Department. It was to prove decisive. He observed that the only way to make the project a success would be to lay a pipe continuously. In Iran, a pumping problem had been overcome by using a 3-inch pipe, working at a high pressure of 1,500 lb/in², to deliver the equivalent of 25,000 cans a day over 40 miles. This solution inspired Hartley.
He contacted the chairman of Anglo-Iranian Oil, Sir William Fraser, and gained his support. The codename Hais was selected. A week later, 200 yards of 2-inch diameter pipe were tested and found able to withstand 700 lb/in² pressure before failing at the plumbed ends. It was thought able to deliver 30,000 gallons a day over 23 miles. Winston Churchill and Lloyd requested urgent development of the project.
Anglo-Iranian, the Post Office, the Admiralty, Combined Operations and the War Office gathered at the department to develop the idea. Siemens Brothers produced a cable and the Post Office ship Alert laid a loop in the Medway on 10 May 1942. Pumps were borrowed from the Manchester Ship Canal Company. However, after two days it failed. Tests by Siemens, the Post Office and Henleys revealed that the failure was due to the extrusion of the lead through gaps left in the spiral steel-tape armouring. Within two days Siemens and Henleys had developed a new specification that could withstand greater pressure. The layers of tapes and wires were designed for right- and left-hand lay respectively so that the cable wouldn’t twist under internal pressure. Further tests were held in the Clyde and Bristol Channel.
It was recognised that special cable ships would have to lay the pipe owing to its weight. A 1,500-ton coaster, HMS London, was loaned by the Ministry of War Transport and the Admiralty and renamed Holdfast. Johnson & Phillips cable gear was lent by the Post Office.
Tests revealed that failure occurred at or near the fittings at the pipe ends because of pressure. It was crucial that suitable fittings for joining the shore ends to the main lengths were found. Experiments resulted in the Hais cable coupling. One feature was that two lengths of cable could be joined together at sea using a split muff coupling that didn’t require bolts.
Combined Operations conducted tests to find ways of handling the shore ends with craft that would be available on D-Day. It was realised that a method of coiling cable horizontally in the hold of a self-propelling barge fitted for paying it out over the stern through hand-controlled compressor gear would have to be used. This involved allocating precious Thames barges and crews for this sole purpose.
The National Oil Refineries, Royal Engineers, Combined Operations and the Royal Army Service Corps (RASC) had erected a pumping station at Queens Dock, Swansea, and a receiving terminal at Watermouth Bay, Ilfracombe, Devon. A German raid at Swansea proved that the cable was not damaged by a bomb falling within 100ft. A ship caught and dragged the cable in a gale but Holdfast was easily able to locate it. The damaged portion was cut out and replaced.
It was realised that increasing the diameter to 3 inches would deliver 2¾ times more petrol. The finished full cable weighed 63 tons per 1.15 miles; it was made in continuous lengths of 40.25 miles. Huge manufacturing capacity was required so Callender, Glover and Pirelli were brought in. Eight 60ft-diameter coiling sites were built to facilitate continuous manufacture. Hartley even enlisted American companies to produce 161 miles of the total 816.5 miles of cable used.
Two engineers from Burmah Oil and Iraq Petroleum (Ellis and Hammick) observed that the Hais cable was flexible at long length yet stiff at short. They had seen the same properties in steel pipes. Tests revealed that 3-inch steel pipe could be bent round; it could be pulled off relatively straight and could be flash-welded to provide any required length. It would be transported in a giant floating drum, or Conun.
There was no proof as to how steel pipe would lie and behave on the ocean floor but six weeks’ life was assumed. Stewarts & Lloyds were charged with the manufacture of the steel Hamel pipe, and a hopper barge (HMS Persephone) was fitted out with six Conuns. Two factories at Tilbury in Essex were erected to carry out production.
Trials on Persephone proved successful. During June and July 1943, Hais cable and Hamel pipe continued to be manufactured, and test pumping was extended to Dungeness in Kent and the Isle of Wight. Three more ships and six Thames barges, with auxiliary vessels, were gathered with a crew of 1,100. Tugs were employed so that 70 miles of pipe could be moved in a Conun (total weight: 1,600 tons).
Two pumping stations on the Isle of Wight were interconnected so that if one was bombed the other could take over. At Dungeness 214 gallons of petrol were delivered a minute. Towing speeds of 7 knots were developed at trials in Bournemouth Bay during April 1944.
Security and camouflage were crucial to success. Pumping station construction was under the supervision of a camouflage officer. Existing structures such as an ice cream factory were used as pump buildings; all plant that might be seen from above was moved at night; and control photographs were taken by the RAF regularly. Hartley described the precautions as expensive and tiresome but there is no doubting their success as no enemy interference occurred.
Operation Pluto began on 12 August 1944. Two sets of Hais and Hamel lines were laid to Cherbourg in France, and pumping began. However, priority was given to the Dungeness-to-Boulogne crossing. Lengths of Hais cable were laid over the stern and the ends dropped to the bottom. These were picked up later when the tide was favourable for connecting the shore ends in the barges. The first Hais-Hamel line was commissioned in January 1945.
Force Pluto laid the lines to the shore, where the Royal Engineers and RASC connected the ends to delivery lines. Telephone links allowed control rooms and pumping stations to know the flow of oil and which lines were in use. In total, 11 Hais and six Hais-Hamel lines were laid with a joint capacity exceeding 4,500 tons a day. Petrol was taken through three land lines of 6-inch Victaulic-jointed pipe to tanks of 1,200-tons capacity. From here, it was pumped to Calais, Ghent, Antwerp, Eindhoven and across the Rhine to further Victaulic lines.
A duplicate system was being laid to guard against submarine attack when Victory in Europe day arrived on 8 May 1945. Pumping continued into July to supply the Far East.
No laid Hais pipelines failed and when the cables were cleared they were proved to be in good condition. The Hamel pipes were not so durable but they did what they were designed to do. The loss of petrol was only 1.1%, and more than 172 million gallons were supplied.
Operation Pluto was remarkable for many reasons: its success rate, its level of co-operation between commercial and governmental organisations, and its ability to target need well beyond the beaches of Normandy