Chief Of Staff to Supreme Allied Commander (COSSAC)

General Morgan begins his task when Lieutenant-General Ismay, the Deputy Secretary to the War Cabinet, presents him with a thick file of papers containing the Combined Commanders’ work on the proposed operations against German forces in Europe. Morgan is required to elaborate on the means by which the expedition will be organized and undertaken within twenty-four hours. This memorandum serves as a basis for discussion when he meets the Chiefs of Staff on March 24^th, 1943.

In the memorandum, Morgan emphasises the importance of combining planning and execution from the outset. He also stresses that there must be complete amalgamation between the British and American services. Morgan believes that the Chief of Staff should have plenary powers to impersonate the commander-to-be temporarily, enabling the organization to maintain momentum until the Supreme Commander’s arrival.

At the first meeting of COSSAC on April 17^th, 1943, Morgan stresses the need for action, not just paper plans. He envisions COSSAC as an embryo of the future Supreme Headquarters Staff and emphasizes the importance of producing the “Master Plan” for the reconquest of Europe.

The Directive to COSSAC, finalised on April 26^th, 1943, outlines the responsibilities for planning amphibious operations from the United Kingdom. The Directive mandates the preparation of plans for deception operations, a return to the continent in the event of German disintegration, and a full-scale assault in 1944.

COSSAC’s history from its inception to its transformation into the Headquarters of the Supreme Allied Commander is marked by the development of three main operational plans and the expansion of its organization and powers. These plans are Operation Cockade, Operation Rankin, and Operation Overlord.

Operation Cockade consists of a series of deception operations to pin the enemy in the West and keep alive the expectation of large-scale cross-Channel operations in 1943. Operation Rankin involves plans for a return to the continent in the event of German weakening or collapse. Operation Overlord is the plan for a full-scale assault on the continent in 1944.

As the time for implementation draws near, the necessity for granting COSSAC executive powers becomes evident. By August 1943, preparations for transforming COSSAC into an operational headquarters are underway. This transformation is crucial for proceeding to detailed planning and for taking the necessary executive action to implement approved plans.

COSSAC’s work involves considerable traveling by its principal staff members to coordinate with other Allied headquarters and to present operational plans to the U.S. Chiefs of Staff and the Combined Chiefs of Staff.

The expansion of COSSAC requires a larger staff and closer integration between the British and American components. By October 1943, a single U.S.-British Operational Branch is formed, and the branches are renamed as “G Divisions.” This reorganisation ensures that COSSAC functions effectively as an operational headquarters.

Civil Affairs, Publicity, and Psychological Warfare become significant branches within COSSAC, reflecting the broadening scope of its responsibilities. The integration of American and British efforts, along with the establishment of effective administrative procedures, ensures that COSSAC can manage the complexities of planning and executing operations.

By January 1944, COSSAC evolves into the Supreme Headquarters, Allied Expeditionary Force, ready for General Eisenhower to assume command. The plans for operations, including Operation Overlord, are prepared, marking the culmination of COSSAC’s work in planning the Allied invasion of Northwest Europe.

Operation Cockade

The Casablanca Conference realises early on that hopes for an invasion of the Continent during 1943 are doomed to disappointment. American forces are not available in the anticipated numbers, and upcoming moves in the Mediterranean absorb nearly all resources essential for amphibious warfare. Despite this, the Prime Minister emphasizes the importance of concealing the true weakness of Allied cross-Channel operations from the enemy. A broad strategic deception policy is needed to threaten the Germans and Italians on multiple fronts, preventing them from reallocating forces to the Russian front and causing them to waste resources on defensive measures.

General Morgan is directed to prepare plans for “an elaborate camouflage and deception scheme extending over the whole summer” to pin the enemy in the west and maintain the expectation of large-scale cross-Channel operations in 1943. Multiple threats are necessary to fully contain enemy forces, not just directly across the Channel, but also against Norway and western France. Resources must be concentrated to create credible threats, using dummies and camouflage to compensate for actual shortages.

The directive requires a substantial deception effort to keep German forces in France pinned down. Past German refusals to respond to unconvincing deception threats in Norway are noted, but it is believed that working from interior lines in the UK, supplemented by dummies and camouflage, can create plausible threats. The Dieppe raid in August 1942 demonstrates that a mere raid is insufficient to pin down German reserves. The Allied air forces aim to provoke the German fighter force into battle to use their superior strength to weaken German air power.

In Norway, the isolated nature of the regions makes it impossible for Germany to move reserves fluidly. The minimum necessary forces hold the country, making it sufficient to threaten any one area to contain enemy forces throughout Norway. In France, the Pas de Calais area is chosen for its suitability for air battles advantageous to the Allies, but a secondary threat in Brittany is also necessary to lend credibility to the primary feint.

By June 3^rd, 1943, the appreciation and outline plans for Operation Cockade are ready. The scheme consists of three component operations: Starkey, Tindall, and Wadham.

The objective of ‘Starkey’ is to convince the enemy of an imminent large-scale landing in the Pas de Calais area, compelling the German fighter force to engage in air battles. The Canadian Army, supplemented by the Marine Division and four Commandos, forms the core of the land forces, with parts of the British 2nd Army creating the impression of a nine-division force. A significant assembly of landing craft on the south coast, including dummies, aims to add realism.

The Allies anticipate a numerical superiority in single-engine fighters and plan concentrated air and sea bombardments to disrupt enemy defenses. The operation is scheduled for early September 1943, with detailed planning and control by the Air Officer Commanding-in-Chief, Fighter Command, in collaboration with other commanders.

Operation Wadham aims to convince the enemy of a planned large-scale operation to capture the Brest Peninsula by American forces in early autumn. The operation culminates on September 30^th, 1943, suggesting it depends on the prior success of Operation Starkey. It involves simulated preparations for a combined seaborne and airborne assault on Brittany, primarily by the American V Corps. The arrival of U.S. troops in Britain is used to create the impression of an intended build-up for the operation.

Operation Tindall aims to threaten Stavanger in Norway, pinning down German forces there during the summer and early autumn. The operation is initially planned for mid-September 1943 but is later postponed. It involves simulated preparations for a heavy-scale airborne attack followed by seaborne forces to capture Stavanger’s port and airfields. The display of real and dummy aircraft and gliders, along with reconnaissance activities, supports this deception.

Operation Cockade is closely linked with Operation Rankin, which plans for Allied forces’ return to the Continent in case of German weakening or collapse. Operation Cockade aims to deceive the enemy and provoke reactions that benefit Allied strategies.

Despite the detailed plans, Operation Cockade does not achieve the expected results. Operation Wadham is primarily a diversion and fails to elicit significant enemy responses due to the lack of actual naval lift. ‘Tindall’ also does not provoke German reactions, and its preparations are unconvincing due to insufficient resources.

Operation Starkey faces challenges with weather disrupting air operations and minesweeping, and the shortage of landing craft reduces its realism. The desired air battles and defensive movements in France do not materialize, and German forces are not significantly pinned down.

Although Operation Cockade does not fully succeed in its deception goals, it provides valuable training and experience for the Allied forces. Operation Wadham helps prepare U.S. forces in Britain, and Exercise Harlequin, part of Operation Starkey, offers essential practice for the eventual Operation Overlord. In these respects, Operation Cockade has some positive outcomes, despite its overall limited success.

Operation Rankin

In the original directive to COSSAC, General Morgan’s staff is tasked with planning “a return to the Continent in the event of German disintegration at any time from now onwards with whatever forces may be available at the time.” These schemes are known as Operation Rankin.

General Morgan outlines the basic principles for this planning in a paper issued to his Principal Staff Officers on May 22^nd, 1943. He emphasizes that the plan must be flexible since the timing depends on the enemy’s actions. The task is akin to preparing a mobilization scheme in peacetime for an unpredictable day, ensuring minimal disruption to normal activities until then. Plans must enable swift action at any moment without interfering with other Allied deception or invasion schemes.

Morgan points out that any German collapse will be sudden, but the Intelligence staff should be able to provide some forewarning for preparations. The disintegration might not be a complete collapse; Germany might withdraw gradually or fight with depleted supplies and reserves. COSSAC must plan for both landing on the Continent and occupying countries under German control.

Initially, in May 1943, available forces make it possible to plan only for a return under conditions of total German collapse. However, as American forces increase, greater risks can be taken, and occupation can be carried out with American support. Meanwhile, British forces will primarily undertake the initial operations, with token U.S. contingents accompanying them. Speed is crucial, and all available resources, including those from training schools and depots, must be used. The focus is on transporting the army to Europe, even at the expense of normal regulations and restrictions.

Plans must also address handling liberated peoples, requiring an effective Civil Affairs organization and contact with European Allied governments in exile. On June 23^rd, 1943, Principal Staff Officers are instructed to consider setting up advanced guards for the occupation forces to enter enemy-held territories promptly when the time comes.

By summer 1943, German weakening or collapse seems imminent, and COSSAC staff prioritises planning for Operation Rankin. Germany might withdraw due to threats from Operation Cockade or pressure in Russia or Italy, necessitating readiness from August 1^st, 1943. If German resistance ceases, the Allies must aim for strategic air bases in occupied territories to support further land operations.

Despite the urgency, planning progresses slowly. By the end of July 1943, Morgan complains of no significant progress, insisting on preparations despite resource limitations. Plans must include continuous reconnaissance, deployment of advanced guards, securing airfields, and coordinating transportation and maintenance.

By August 13^th, 1943, COSSAC submits basic plans for Operation Rankin to the British Chiefs of Staff. The plans address potential scenarios: “Rankin” Case A for a substantial weakening of German forces, Operation Rankin Case B for a German withdrawal, and “Rankin” Case C for an unconditional surrender by Germany. In Case A, the objective is to secure a limited lodgment on the Continent for further operations. In Case B, the Allies must occupy vacated areas without being tied down far from future action centers. In Case C, the focus is rapid occupation and enforcement of surrender terms.

In “Rankin” Case A, an assault against weak opposition is feasible from January 1944 onwards, targeting the Cotentin Peninsula and Cherbourg. Diversionary operations may be necessary in Pas de Calais and southern France. In “Rankin” Case B, the Allies need to occupy vacated areas in Norway and western France, with the main entry through Cherbourg. In “Rankin” Case C, rapid occupation of key areas in Germany and liberated countries is essential, requiring 24 divisions for primary areas of occupation and support troops for rehabilitation efforts.

The plans are approved at the Quadrant Conference in August 1943, with detailed planning proceeding. There is debate over prioritizing Case A or C, with COSSAC favoring Case C. By October, Case C is prioritised, and directives are issued for detailed preparations. Special plans for Norway and the Channel Islands are also drafted.

Operation Rankin is closely linked to Operation Cockade and Operation Overlord. Threats from Operation Cockade could lead to German withdrawal, creating “Rankin” Case B conditions. Case A resembles a modified Operation Overlord plan, merging with preparations for the larger invasion. The possibility of German collapse post-Overlord also aligns with Case C. The Operation Rankin plans remain flexible, ready to exploit any enemy weakening.

By January 1944, detailed preparations continue, focusing on Civil Affairs and dealing with populations in occupied and German territories. However, the likelihood of “Rankin” conditions arising before Operation Overlord implementation diminishes. German resilience in Italy and Russia suggests that a full invasion is necessary to force a German retreat or collapse. Operation Rankin thus becomes a subsidiary to Operation Overlord, guiding steps after the initial success of the mass Allied invasion.

Operation Overlord

In it’s third and last task, COSSAC is tasked with preparing a full-scale assault on the Continent in 1944, now known as Operation Overlord. Prior to COSSAC’s creation, the Combined Commanders discussed the difficulties of returning to the Continent. General Morgan’s staff must now shift from a strategy of attrition to planning for a decisive, knockout blow against Germany. With increasing American forces arriving in Britain, it is essential to prepare for a rapid and overwhelming invasion.

The plan involves launching the attack from the United Kingdom, targeting Northern France and the Low Countries. Anglo-Canadian armies will be based in Southeast England, with American forces to the west. These groups will make the initial assault, followed by American reinforcements sailing directly from the United States to secure a bridgehead. The goal is to amass around 100 divisions on the Continent to crush German power.

On May 25^th, 1943, the Combined Chiefs of Staff issue a supplementary directive to COSSAC, aiming to secure a lodgment on the Continent from which further operations can be launched. Plans are to be developed for capturing and developing continental ports, allowing additional forces to be shipped in at a rate of three to five divisions per month. The target date for the operation is set for May 1^st, 1944, with outline plans due by August 1^st, 1943.

During June and July 1943, planning based on these resources continues. With limited landing craft, dispersion is not an option. The main alternatives considered for the assault are the Caen and Pas de Calais areas. Both have difficulties, but Allied naval and air supremacy is expected to mitigate these. The British and U.S. Naval Sections prepare plans to protect the attacking forces, while the Air Sections work on securing air superiority. Army Operations Sections, with naval assistance, develop plans for the assault forces.

The crucial factor in choosing the initial assault location is ensuring sufficient port facilities to support up to 30 divisions. The Pas de Calais offers proximity to England and quick turnaround for shipping but has strong defences and poor exits. The Cotentin Peninsula, while promising, lacks suitable airfields. The Caen sector, with light defenses, high-capacity beaches, and suitable terrain for airfields and expansion, is chosen. The aim is to capture the Cherbourg-Brittany ports for the build-up.

Success depends on reducing the German fighter air force and limiting their mobile divisions in France. The number of Allied landing craft is low, necessitating a 10 percent increase and possibly the creation of artificial harbors for beach maintenance. The preliminary phase involves actions to weaken German air forces and morale, with diversionary operations to mislead them.

During the preparatory phase, intensified air action targets airfields and communications. Three naval assault forces gather in southern England, with two more in the Thames Estuary and on the west coast. The assault begins with air bombardment, followed by landing three assault divisions on the Caen beaches, with airborne forces capturing Caen itself. Commandos and airborne units neutralise coastal defenses and seize river crossings, aiming to secure the Grandcamp-Bayeux-Caen line.

Subsequent operations involve advancing south and southwest to destroy enemy forces, establish airfields, and prepare for a thrust into the Cotentin Peninsula to capture Cherbourg. Within 14 days, the goal is to take Cherbourg and extend the bridgehead to the Trouville-Alençon-Mont Saint Michel line, landing 18 divisions and operating 14 airfields. Further operations depend on the enemy’s reactions. If weak, an advance to seize Havre and Rouen is possible. Otherwise, capturing Brittany ports first will be necessary to build up forces to breach the Seine line. A thrust southward to Nantes and Saint Nazaire, followed by Brest and other ports, will consolidate the left flank along the Eure and Seine rivers, preparing for operations against Paris and the Seine ports.

By August 1943, the “Overlord” plan is ready and presented at the Quadrant Conference. Despite concerns about resources and optimism, the outline plans are approved. COSSAC continues planning and preparations, now recognized as the primary task facing the Allied forces. By November 29^th, 1943, directives for the operation are issued to 21^st Army Group and 1^st U.S. Army Group. The Supreme Allied Commander coordinates the overall execution, with the initial assault led by a composite army under unified command. The buildup of American troops in the UK accelerates, aiming for 1,000,000 men by the end of 1943 and 1,250,000 by March 1944.

Despite intensive training, battle-experienced formations from North Africa are needed for the initial assault. Proposals for utilizing these troops are approved, and plans are made for their return to Great Britain for Operation Overlord. The greatest difficulty lies in providing sufficient landing craft. Efforts to increase production continue, but by September 1943, the shortage remains critical. General Morgan emphasises the need for a balanced buildup of assault and follow-up forces. By January 1944, Supreme Headquarters Allied Expeditionary Force is established, and General Dwight D. Eisenhower assumes command, transforming COSSAC into Supreme Headquarters Allied Expeditionary Force (SHAEF).