Planning and Preparation of Overlord and Neptune

Combined Operations pre-WW2

Prior to WW2, there had been limited interest in specialised amphibious warfare techniques by the British Services, despite the maritime strategy that underpinned the Empire. This largely reflected the lack of need during pre-industrial warfare for specialist craft - if need be, infantry could always be landed relatively easily from standard shipping and the short range and limited firepower of weaponry gave coastal defenders no great advantage, provided they chose their landing points carefully. The first real attempt at an amphibious assault in the modern context had been at Gallipoli with improvised craft to reduce the water gap. More coherent and specialist modifications to shipping were made for the Zeebrugge raid on St George's Day in 1918, with careful rehearsal and training.

However, in 1939, amphibious operations were still seen as largely a Royal Marines responsibility with a strictly limited scope in support of RN operations. That said, the three Staff Colleges held an annual Combined Operations study period each year and the important step had been taken in 1938 to establish a small Inter-Services Training and Development Centre (ISTDC) at Fort Cumberland, Eastney, Portsmouth, manned on a Tri-Service basis, to examine amphibious and airborne assault techniques, and the specialised shipping that would be required.

WW2 - The Early Days

The Royal Navy started the war with just 24 small landing craft, which had been built in small batches since 1927. All were lost during the Norwegian campaign in the Spring of 1940. However, new Landing Craft Assault and Landing Craft Mechanised, built to ISTDC requirements, were under construction, with 11 completed in time to help during the Dunkirk evacuation - six were lost.

Immediately following the fall of Europe, Churchill immediately demanded the start of work to allow the eventual re-entry of British forces to the continent. Thus in June 1940, Lt Gen Sir Alan Bourne RM was appointed Commander of Raiding Forces. At the same time, Lt Col Dudley Clarke RA developed a Commando warfare concept for harassing the enemy and the Army duly began forming the first Commandos, drawing on a number of Independent Companies raised for the Norwegian campaign. (The first Royal Marine Commandos were not formed until 1942.) A Landing Craft depot and training school was established on Hayling Island as HMS Northney and Bourne's organisation was able to launch its first cross-Channel raid on 24 June 1940. Although the only casualty was Lt Col Clarke, who was wounded, the experience demonstrated the need for specialist training for landing craft crews and assault troops, and the need for purpose-built equipment.

Admiral of the Fleet Sir Roger Keyes, the architect of the Zeebrugge raid, was brought back from retirement by Churchill to supersede Bourne in July 1940. (The latter was double-hatted as Adjutant-General RM and was needed to concentrate on the expansion of the Corps.) Keyes established the Directorate of Combined Operations or DCO in Richmond Terrace, Whitehall. The first Combined Training Centre was established at Inveraray, opening on 1 September 1940 under Vice-Admiral Hallett. Keyes' command initially comprised 750 men in Independent Companies, 500 men in the first Commando units starting to form up, and 19 LCAs and LCMs.

Under Keyes, the DCO was involved in much planning work for potential operations against targets such as the Canary Islands, the Azores and Pantellaria, absorbing lessons from early raids and the failed attempt to seize Dakar from the Vichy French, and laying the foundations for the expansion of Combined Training. Keyes resigned in October 1941 after a major disagreement with the Chiefs of Staff over a major training exercise. In his place, Commodore Lord Louis Mountbatten was appointed as Adviser on Combined Operations. The DCO became Combined Operations Headquarters (COHQ).

COHQ

COHQ was responsible for planning the successful raids on Vaagso, Bruneval and St Nazaire conducted between December 1941 and March 1942. COHQ was also involved in the start of planning work by CinC Home Forces for the re-entry into Europe. The first such plan, for "a large-scale raid of some duration" was codenamed Sesame. This was quickly followed by Sledgehammer (an emergency assault to distract the Germans if they looked like overwhelming the Soviets) and Round-up, a full-scale invasion of Occupied Europe. Round-up proved to be the genesis of Overlord, the overall plan to liberate Europe. Within Overlord, the amphibious operation to land in Normandy was to become known as Neptune.

Mountbatten was promoted Vice Admiral in March 1942 and re-titled as Chief of Combined Operations (CCO), becoming a member of the Chiefs of Staff committee. Around this time, a COHQ liaison officer was dispatched to Washington, and Brigadier Sir Harold Wernher was appointed Coordinator of Ministry and Service Facilities. His task was to bring together all the different Departments and Ministries needed to support large-scale amphibious preparations. An important early job was a detailed examination of every port between the Wash and the Bristol Channel to catalogue all available berths, and the identification of areas within 30 miles of the coast where an invasion army could be assembled. As a result of his work, a major expansion programme for camps, roads and vehicle hard-standings commenced.

Dieppe

The initial plans for Round-up assumed that divisional-level assaults on ports would be needed. It was recognised that such a demanding task needed to be tested. Thus planning began for Operation Rutter, with the French port of Dieppe selected as the target for a major raid. The large number of Canadian forces mustering in the UK were keen to see action, and 2nd Canadian Division was selected. Full-scale rehearsals were conducted in June, but bad weather forced the cancellation of Rutter. However, it was resurrected as Operation Jubilee, and mounted on 19 August 1942.

The loss of around half the assault force has led Jubilee to be described often as a failure. However, the lessons learnt proved invaluable in the shaping of the concept for the invasion of Europe. These included:

• A frontal assault on a defended port was not practicable.
• Standard naval vessels alone could not provide all the gunnery support needed close inshore during an assault.
• Well-trained and efficient beach parties were needed to organise the arrival of men and equipment on the shore under enemy fire.
• Methods of clearing underwater obstacles had to be developed.
• Methods were needed for getting tanks ashore safely and off the beach.
• Landing troops in precise locations required specialist skills in beach recognition and inshore navigation.
• Dedicated headquarters ships, fitted out with extensive radio equipment, were needed to provide command and control of the assault.
• Fighter Direction ships, fitted with radar and appropriate radio communications, were needed to coordinate air support directly over the fleet and beaches.
• Landing craft forces needed to be assembled, trained together and kept as a coherent force, rather than being organised ad hoc.

Torch and Husky

COHQ was heavily involved in the planning for the Torch landings in North Africa, conducted on a large scale but facing only limited opposition from Vichy French defences.  A more challenging operation was the Husky landings in Sicily, which drew heavily on the lessons of Dieppe and the specialised landing craft and techniques now being developed. For example, Combined Operations Pilotage Parties, including Royal Navy navigation specialists and Royal Engineer officers, had been formed, trained to conduct night beach reconnaissance missions from submarines and provide pilotage for the leading landing craft during the assault. The Beach Pilotage School was HMS James Cook at Glen Caladh, Tighnabruaich.

Beach Commandos and Beach Groups were also available to organise the flow of men and equipment across the beaches, with a school established as HMS Armadillo at Ardentinny on Loch Long. That said, some of the Beach units used in Husky were locally trained in the Mediterranean, which led to some differences in doctrine. With regards to the widening variety of landing craft available, two types modified to act as inshore gunnery platforms made their operational debut, the LCG armed with a pair of 4.7" guns and the LCT(R), each armed with 1,044 5" rockets to be fired in salvos in a crash area shoot during the final assault run-in. The US-built DUKW amphibious trucks proved tremendously valuable and became a key component for Overlord-Neptune.

Overlord-Neptune Planning

Meanwhile, much work continued to assemble topographical detail on the French coast, including the examination of pre-war holiday photographs. RAF reconnaissance aircraft systematically photographed beaches at every state of tide, allowing initial assessments of beach gradients to be made. To tackle the problem of delivering the massive quantities of fuel that an invasion army would need, the development of what became Pipeline Under The Ocean (PLUTO) was underway, using cable-laying ships to position flexible piping in 35-mile lengths capable of passing 100 tons of fuel per day per pipe. The pipes could be laid at a speed of about 4 knots.

Dedicated manpower was a problem - the landing craft crews needed would number up to 30,000, all requiring intensive training. This was partly met by disbanding the Royal Marine Division - its infantry battalions were re-roled as Royal Marine Commandos, with the other personnel taking on the manning of many of the smaller assault craft.

The detailed shaping of the invasion plans fell to the Chief of Staff to the Supreme Allied Commander (COSSAC) and his staff. The decision on who would be the Supreme Allied Commander was deferred - General Eisenhower was eventually appointed on Christmas Eve, 1943 - but from the Spring of 1943, the Chief of Staff post was filled by Lieutenant-General Sir Frederick Morgan. The COSSAC team was very much a joint UK-US planning staff, and drew upon the expertise developed by COHQ.

COSSAC quickly narrowed the choice for a potential invasion area to either the Pas de Calais or the Caen sector of Normandy. The Pas de Calais offered the shortest sea and air crossing, and also was closer to the borders of Germany itself. However, it was an all-too obvious target, and was very heavily defended by the Germans. Furthermore, the ports in the Dover area were too small to accommodate the invasion fleets, while the beaches at Calais were very difficult, being narrow and backed by high cliffs with few exits.

In contrast, the Normandy beaches were less strongly fortified, partly sheltered from the prevailing westerly winds, and better suited to the landing of vehicles and supplies. A major port, Cherbourg, lay within reasonable striking distance for it to be secured after the landings. However, at 100 miles from the English coast, Normandy posed greater difficulties for a safe crossing by landing craft and the maintenance of air supremacy, since fighters could spend far less time on station.

The build-up of US forces in Britain was of course well underway, with 1.5 million men brought across the Atlantic by May 1944 - 425,000 in the Queen Mary and Queen Elizabeth liners alone, each carrying 15,000 per run - along with 5.25 million tons of stores. To provide air support to the invasion armies, the Royal Air Force formed the 2nd Tactical Air Force in November 1943, with fighters, fighter-bombers, light bombers and reconnaissance aircraft. 2TAF drew on the techniques developed in the Western Desert to form mobile teams of ground personnel who could quickly establish airfields in captured enemy territory, and Army-RAF liaison teams working in the front-line to direct fighter-bombers onto specific targets. The US Ninth Air Force also adopted a tactical role, again equipped with fighters and light bombers.

The Mulberries and Gooseberries

A key part of the plan was the construction in secret of two prefabricated Mulberry harbours. Given that the immediate capture of a major port had been ruled out following the experience of Dieppe, the audacious solution was for the invasion force to take its own harbour with it. In one of the most remarkable achievements ever of British engineering, huge concrete and steel structures were built around the south coast of England which could be towed across the Channel and assembled to form two large harbours, each the size of Dover, off the Normandy coast. Mulberry A would support the US forces at St Laurent, while Mulberry B would support the British and Canadians off Arromanches. Very careful survey work of the seabed had to be conducted covertly by the Combined Operations Pilotage Parties working from midget submarines and small boats during the hours of darkness along the German-held coast.

The Royal Navy took responsibility for designing the Mulberries' outer sea defences, consisting of old ships scuttled as breakwaters and 200 feet long floating concrete Bombardons weighing 2,000 tons apiece. The Army designed the huge 6,000 ton concrete Phoenix caissons to form the main harbour walls and the Whale system of mile-long floating piers which would rise and fall with the tide, onto which vehicles could be unloaded and driven ashore. 23,000 men were employed building the pieces at some fifty sites. 200 tugs were involved for three months towing the various components to muster points on the coast between Dungeness and Portland, ready to follow the invasion fleet across the Channel.

It was never imagined that the Mulberries would handle all the invading forces' needs, but they would offer the ability to unload particularly heavy or bulky loads, such as engineering equipment. Most of the smaller equipment and supplies, plus men, would still have to be landed across the beaches for some considerable time after D-Day. The Mulberries were therefore complemented by the five Gooseberries - groups of old ships sunk as breakwaters off of each of the five invasion areas. These would provide some shelter to the smaller landing craft in rough weather, and since the ships' superstructures would still be above water once sunk in place, they could be used as temporary accommodation for the landing craft crews. The two Gooseberries at Omaha and Gold would in due course be incorporated into the Mulberries.

The Transportation Plan

Once the Allied forces were ashore in Normandy, the challenge would be to build up their numbers faster than the Germans could match them. Given that the Allied troops had to come across the Channel, while the enemy had road and rail networks in Europe at its command, this might indeed prove difficult. Everything that could possibly be done to disrupt these networks and slow down the movement of German reserves was therefore judged critical.

A major air offensive, the Transportation Plan, therefore commenced in the Spring of 1944, despite the reservations of the strategic air commanders. Rail tracks were relatively easy to repair, so major nodal points in the railway system, such as marshalling yards, engine sheds and repair facilities were the primary targets. Unfortunately, these all too often lay in urban areas of Occupied Europe. Fatalities amongst the French, Dutch and Belgian inhabitants were thankfully low on most occasions, but remained a major worry, especially to Churchill. Some eighty major targets were attacked and slowly the railway network in northern France and Belgium was paralysed. A fortnight before D-Day, on 21 May, over 1250 Allied fighters were unleashed to sweep across Western Europe and attack any trains that could be spotted. Hundreds of locomotives and rolling stock were destroyed or damaged. Bombers also began targeting key bridges and known military facilities. Although the effect was to increasingly isolate Normandy, the targets were carefully chosen as not to point to that as the primary area of interest; for every target attacked in that area, two were attacked further afield.

A gun-camera photograph of rockets from an RAF Typhoon fighter-bomber streaking towards a German position on the French coast on 5 June, the day before D-Day.

In the ten weeks leading up to D-Day, Allied aircraft flew over 200,000 sorties and dropped nearly as many tons of bombs. The cost was high, nearly 2,000 aircraft and crews being lost. However, complete air superiority had been established - only two German aircraft appeared over the beaches on D-Day. The radar stations along the coast had been systematically targeted and were largely out of action.

Last Updated: 22 Jun 04