Some of the oil needed to support the Allied advance across France was carried by the imaginatively named PipeLine Under The Ocean, or PLUTO for short - though some sources suggest PLUTO stood for Pipeline Underwater Transportation of Oil. The development of PLUTO was driven by the voracious need of modern militaries for petrol, to supply tanks, trucks and aircraft. The Allied military forces landed in France would need thousands of gallons of petrol. Until a port was captured, there was nowhere for tankers to offload this fuel - and most of those available were too small. Carrying the fuel in tankers would also put considerable stress both on the Allied tanker fleet, and on the systems set up to control traffic in the Channel. Finally, the tankers would be vulnerable to air and submarine attack. Landing the petrol across the beaches in jerry cans was an absurdity, given the scale of the operation. To solve this problem, an undersea pipeline was an obvious solution.

The idea was a British one, dating back as far as 1942. The British Combined Operations Headquarters, which was responsible for amphibious landings, had been grappling with the idea of fuel supply to any cross-channel invasion, and had hit upon the pipeline concept. In early 1942, Lord Mountbatten (commanding Combined Operations) met with Geoffrey Lloyd MP (minister for Petroleum Warfare, and the man who set British fuel policy) and representatives from the oil industry to discuss the concept. While there were existing methods for laying underwater pipelines, these were deemed to be unsuitable. They were either too slow, or relied on support infrastructure that was deemed to be vulnerable to bombing. However, a Mr Hartley, the chief engineer of the Anglo-Iranian Oil Company, suggested that submarine telephone and telegraph cables might, without the copper core, be useful for this purpose. This could be laid quickly, as the cables were flexible, without much infrastructure (using already existing cable ships), and was fairly easy to produce. The 'cables' were produced by the Siemens company. They initially consisted of a 2" lead pipe, surrounded by two layers of galvanised steel strips and bound up with steel wire. Later versions increased the pipe width to 3", wrapped in layers of paper and cotton tape, four layers of steel tape and a layer of steel wire as a binding, with jute wrapping over the top. The cables were given the codename HAIS, from the initials of the three main participants (Hartley, Anglo-Iranian Oil, and Siemens). The first trial came in May 1942, when the cable ship Alert laid a short length across the River Medway. This proved successful, and after refinement, the trials moved north for deep-water testing in the Clyde.

There were problems with the HAIS system, though. The HAIS pipelines were complex to construct, requiring many complex joins made by skilled craftsmen. There were also concerns about the supply of lead. Fortunately, two of the engineers working on the project recalled that sufficiently long lengths of thin steel pipe were flexible enough to be rolled and deployed like a cable. These two engineers (Mr Hammick and Mr Ellis) would give their name to this system, which was dubbed HAMMEL. The steel pipe could not be rolled as tightly as the HAIS cables, though, so larger drums were needed. HAIS cable could be laid by a cable ship, but HAMEL pipes required a massive drum (soon dubbed a Conundrum) towed by a tug. Constructing both systems in the vast lengths needed was a massive undertaking. HAIS cables could be produced by firms experienced in cable-making. Most of the work on the project was carried out by W T Henley in Gravesend and Glovers Cables in Trafford Park, Manchester (near me), but there were contributions from companies in both Britain and America. Of the 710 miles of HAIS cable produced, 570 were made in the UK and 140 in the USA. The HAMEL pipes were easier to produce. Most of them were made by the British Stewarts & Lloyds company in Corby and Glasgow, but again there were contributions from elsewhere. Four ships were taken up from trade and converted to deploy HAIS cables. Five Conundrums were constructed for the HAMEL systems, each displacing 250 tons.

The original planning for PLUTO was based on the assumption that the landings would take place in the Pas de Calais, close to the UK. However, given that this was heavily fortified, the plans moved to Normandy. This more than doubled the length of pipeline required. To minimise the length to cover, the planned route would run from the southern tip of the Isle of Wight to a landfall near Cherbourg, once this was captured. The route was given the codename Bambi. Once the Pas de Calais had been captured, the shorter route could be used, under the codename Dumbo. A terminal for the British end of Dumbo was prepared near Dungeness in Kent. Both the Dungeness and Isle of Wight terminals were joined to the country-wide GPSS pipeline system. As this plan left the troops unsupplied with petrol until Cherbourg had been captured and PLUTO established, a new scheme was developed to allow tankers to be used to supply troops without a port. Named TOMBOLA, it used relatively short (1km) lengths of submerged or floating pipeline, which linked tanker anchorages to shore depots.

TOMBOLA systems were set up at Port-en-Bessin and Ste. Honorine fairly quickly after the landings, and saw fair success. While they were useful, the pipes had a tendency to suffer damage from rocks along the foreshore. To supplement this, small tankers were brought alongside in Port-en-Bessin harbour. PLUTO, though, had to wait until Cherbourg fell. While the original D-Day plans had envisaged this happening on D+8 (i.e 8 days after D-Day), they instead had to wait until D+21. The port had also been wrecked by the Germans. This delayed PLUTO's entry to service, as did considerable bureaucratic wrangling. The first PLUTO pipeline to be deployed was a HAIS cable, laid on August 12th 1944. Unfortunately, the cable was broken very shortly afterwards when a warship caught it with its anchor. A second attempt on the 14th ended similarly. Attempts to deploy the HAMEL pipes, meanwhile, ran into trouble due to a lack of winches to haul the pipe up at the French end. It was not until the 22nd of September when a HAIS cable was successfully deployed, while the HAMEL system had to wait until the 29th. These had a reduced capability over what was originally planned, as pressure in the system was low. Attempts to increase the pressure at the start of October failed, with both pipelines rupturing. Very little oil was transferred through the Bambi route, with less than 5,200 tons being received to France.

By this time, though, the Pas de Calais had been captured, and pipe-laying for the Dumbo route could commence. The first HAIS cable was laid on the 10th October, but bad weather delayed the start of operations until the 27th. By December, five more cables had been laid, but two of these would fail. Again, pressure in them was low, with typical pressures of 20-30 bar compared to the planned 99 bar. This resulted in low throughput, with only 700 tonnes/day being delivered against an originally planned 3,300. The scheme was seen as something of a wasted effort, but in January 1945, it was decided that all possible pipelines should be deployed, in the hope that the planned figure could be reached. Over the coming months, five more HAIS cables and six HAMEL pipelines would be deployed, though some of these would only enter service after VE Day. The system was never very successful, even with these additions. By the end of the war, only 8% of the fuel arriving in Europe was carried by PLUTO; the remaining 92% mainly came in tankers.

PLUTO was an impressive technical feat; an easy and quick-to-deploy pipeline system, that worked at depth, and covered such great distances was an incredible feat of logistics. Ultimately, though, the system never lived up to its promise. The pipes were too heavy, too vulnerable, and too unreliable. They never carried the volume of fuel necessary to support the Allied armies, and took up a great quantity of strategic materials. Had they been more reliable, then the logistical constraints on the Allied advance into France and Belgium would have been greatly reduced.