The British War Office estimated that petrol, oil, and lubricants would account for more than 60 per cent of the weight of supplies required by the expeditionary forces.

Deployment of Bambi began on 12 August 1944, and it delivered just 3,300 long tons (3,400 t) between 22 September, when the first pipeline became operational, and 4 October, when it was terminated.

In early April 1942, the Chief of Combined Operations, Vice-Admiral Lord Louis Mountbatten, approached the Secretary for Petroleum, Geoffrey Lloyd, and asked if an oil pipeline could be laid across the English Channel.

[1] Mountbatten was tasked with planning the Allied invasion of German-occupied Europe, and had concerns about the supply of petroleum products, since it was considered unlikely that a port with oil reception facilities could be quickly secured.

[2] The British War Office estimated that 60 per cent or more by weight of the supplies of the expeditionary forces would consist of petrol, oil and lubricants (POL).

[1] Pipelines were not the sole or even the principal means by which Combined Operations was contemplating supplying bulk petroleum; it intended to rely primarily on small shallow-draught coastal tankers, of which thirty were under construction.

Submarine pipelines were less susceptible to enemy air attack and the frequently stormy English Channel weather, and their use would reduce the forces' dependency on vulnerable storage tanks ashore.

[6] Lloyd consulted his expert advisors: Brigadier Sir Donald Banks, the director-general of the Petroleum Warfare Department; Sir Arthur Charles Hearn [de], a former director of the Anglo-Iranian Oil Company and the oil advisor to the Fourth Sea Lord; and George Martin Lees, an eminent geologist.

[9] The Chief Engineer of Anglo-Iranian, Clifford Hartley, was visiting the Petroleum Warfare Department at this time, and he heard about the proposal, and was convinced that it was possible.

On 15 April he pitched his proposal for a continuous length of pipeline similar to a submarine communications cable without the core and insulation, but with armour to withstand the internal pressure, which could be deployed by a cable-layer ship.

Royal Navy Captain John Fenwick Hutchings from the Admiralty's Department of Miscellaneous Weapons Development was placed in command of Operation Pluto.

[13] Hartley received support for his proposal from the chairman of Anglo-Iranian, Sir William Fraser, who was also the petroleum advisor to the War Office, and from Henry Wright, the managing director of Siemens Brothers.

A 30-mile length was laid across the Bristol Channel in rough weather at a rate of 5 knots (9.3 km/h) with the shore ends being connected at Swansea and Ilfracombe.

Bernard J. Ellis, the chief engineer of the Burmah Oil Company, was convinced that a flexible pipeline could be built from mild steel, which was more readily available than lead.

[27][28] The Petroleum Warfare Department proposed that it be wound around a buoyant steel drum that could be towed by tugs or fitted on a Hopper barge.

[28] Stewarts & Lloyds undertook to design, construct and operate two factories at Tilbury where 40-foot (12 m) lengths of pipe were welded together into 4,000-foot (1,200 m) segments.

At the end of each 4,000-foot (1,200 m) segment, the next was welded, the swarf was cleaned out, and the process continued until the Conundrum held 90 miles (140 km) of pipe, at which point it had a displacement of 1,600 long tons (1,600 t).

The pumping stations and storage tanks were camouflaged to look like villas, seaside cottages, old forts, amusement parks and other innocuous features.

[37] The discovery of an additional German division in the vicinity in May led to the expected capture being pushed back ten days from D+8 to D+18.

[38] In the event, the port of Cherbourg was captured on 27 June (D+21),[39] and due to the extensive damage the first POL tanker did not discharge there until 25 July (D+49).

An attempt to lay Hamel pipe instead failed on 27 August when it was discovered that tons of barnacles had attached themselves to the bottom of HMS Conundrum 1, thereby preventing it from rotating.

[43] Sir Donald Banks wrote: "The technique of cable laying had been mastered but we were not yet sufficiently versed in the practice of connecting the shore ends, nor in effecting repairs to the undersea leaks which were caused fairly close inshore through these faulty concluding operations.

[42] However, on 3 October when the pressure was increased from 50 to 70 bars (730 to 1,020 psi) to augment the amount of fuel pumped,[41] both pipelines failed: the Hais due to a faulty coupling, and the Hamel when it encountered a sharp edge on the ocean floor.

Even when it was cleared the channel from Le Havre was shallow, but coastal tankers carrying POL from the UK were able to navigate it and discharge in Rouen.

[51] As the fighting moved on to Germany, Dumbo was connected to an inland pipeline system that was extended from Boulogne to Antwerp, Eindhoven and ultimately Emmerich.

[55] Although the pipeline itself is no longer in use, many of the buildings that were constructed or utilised to disguise it remain, especially on the Isle of Wight, where the former pumping station at Sandown is currently in use as a miniature golf facility.

Samuel Eliot Morison, the United States naval historian, noted that the pipelines "proved very useful for supplying the Allied armies as they advanced in Germany.

"[57] According to the civil official historian, Michael Postan, Operation Pluto was "strategically important, tactically adventurous, and, from the industrial point of view, strenuous".

[58] On 24 May 1945, Winston Churchill described Operation Pluto as "a wholly British achievement and a piece of amphibious engineering skill of which we may well be proud.

"[43] A similar sentiment was expressed by Major-General Sir Frederick Morgan, the head of the COSSAC staff, who considered that Bambi was not worthwhile, although he lauded Dumbo.