Adopt the outlook that Operation Overlord is even now in progress.
—Lt. Gen. Sir Frederick Morgan, COSSAC, to the British Chiefs of Staff, July 15, 1943
The elements from which the plan for an Allied return to Europe could be assembled began to emerge on June 3 in London when Lieutenant General Morgan was allowed to read the report on the just-completed Trident Conference. Immediately Morgan communicated to his staff from memory, with documents en route by courier, both welcome new information on the resources to be provided and the new name for the operation, Overlord.1 Four days later, Morgan followed up with another memorandum with confirming, amplifying details. The essence of the plan that COSSAC ultimately would produce started to take shape.2
For Overlord, the cross-Channel attack-based strategy, COSSAC was told to plan for an initial force of twenty-nine Allied divisions. There were to be landing craft sufficient for an initial assault on the French coast by five divisions, three Anglo-Canadian and two American. Of these, one British, one Canadian, and one American division would be in the initial landing with one British and one American division aboard ships for immediate follow-up. The objective of the twenty-nine divisions was to establish a lodgment in Europe. This amphibious endeavor, imbedded within Overlord, would be named Operation Neptune. With the lodgment established, the buildup on the Continent then would continue with three to five divisions arriving each month from the United States for the breakout and thrust across northwest Europe into Germany.
The apportionment of divisions to assault function by nationality had been a political decision that also influenced operational planning. Fulfilled was the political mandate that the national armies fight side by side, while avoiding an impractical crossing of lines of communication and logistical supply. This was done through a right flank/left flank assignment, looking from the sea south into France. Envisioned was “a Southwestward thrust by the American forces, covered to the East and Southeast by operation of the British Armies.”3 More precisely, composition of the latter would be Anglo-Canadian.
COSSAC planners learned from the Trident report that “a considerable body of troops, both American and British, battle hardened in the campaigns of North Africa, shall be transferred from that theatre to the United Kingdom in time to take part in Operation OVERLORD.”4 This crucial enhancement to the fighting qualities of the assault force combined with the limited number of divisions for which amphibious lift could be provided shaped COSSAC’s planning in major ways.
Up to that time, the expected qualitative disparity between unproven Allied assault troops and defending German land forces had tended to favor selecting the closer Pas de Calais. By landing at that point nearer to England, the planners hoped, the numerically superior but short-ranged Allied fighter forces could achieve air supremacy, which in combination with shorter turnaround times for ships bringing reinforcements would compensate, they hoped, for the disparity between the Allied troops’ combat experience and that of the enemy. This was perilously thin logic, recognized as such by the planners.5
The Germans could study maps equally well. COSSAC’s estimate from Allied intelligence was that the Germans had transformed the Pas de Calais into “the most strongly defended area of the French coast and the pivot of the German coastal defense system.”6
The anticipated leveling of the fighting qualities of opposing land forces, which would result from the Trident-authorized transfer of battle-tested Allied divisions, freed COSSAC to expand its options. Flying range constraints would limit time over the alternative beachheads and thus the impact of Allied fighter aircraft. Now, however, the availability of more experienced ground troops allowed planners to accept the lesser criterion of air superiority, not supremacy, in order to expand their consideration of landing areas farther afield than the Pas de Calais.
At the same time, the amphibious lift available would constrain the initial assault to only three divisions. From that, Morgan deduced that “we must rule out of count immediately any question of dispersion of effort. The subdivision of so small an assault force as three divisions will inevitably lead to grave risk of defeat in detail.”7 Entertainment of multiple simultaneous landings was out.
Although there were alternative options specific to the Normandy coast, the basic choice for the supreme Allied commander was emerging as entry into northwestern Europe at one place, either through the Pas de Calais or Normandy. To develop that, Morgan directed that “the first task of our Air Sections is to appreciate the possibility of creating by [May 1, 1944] an acceptable air situation in an alternative area, which we know from prior examination to be that of the coastal strip lying between Cherbourg and Dieppe.”8
Barely below the surface was the COSSAC team’s initial qualified reaction to the new knowledge of the resources to be available. The margin for success with forces and tactics to a degree untested would be very thin. They worried that a five-division assault force, even one composed of combat-experienced troops, might not be sufficient to succeed, and they wished for more troops and the craft from which to land them.9
In COSSAC’s view, the larger challenges to increasing the striking power for the cross-Channel attack were those within the Allies’ span of control. These would be obtaining more ships, landing craft, fighters, and transport aircraft, plus achieving and sustaining supply and force buildup through damaged ports and over the beaches. Indirectly within Allied control, through the aerial striking potential of the Allied bomber force, well escorted over France, would be reducing the strength of the opposing German air force by D-Day and limiting the rate at which German reinforcements could reach the invasion area. Myriad other factors affected each perspective on the problem.
Concluding his new appreciation of resources available and their implications on June 7, 1943, Morgan reminded COSSAC planners of the time remaining. If the outline plan for Overlord was to reach the CCS in Washington on schedule, August 1, Morgan would need to submit the plan to the approval process with the British COS Committee in London thirty-three days hence.10
Still, agreement on an outline plan for Overlord refused to emerge from the complex mass of variables and conflicting opinions. To facilitate a solution, Vice Adm. Lord Louis Mountbatten, the chief of Combined Operations, proposed to Morgan a conference, dubbed Rattle, for COSSAC and the men who would be the operational commanders of the invasion forces. For the purpose, Mountbatten offered Combined Operations’ training center in the requisitioned Hollywood Hotel in Largs, a seaside resort west of Glasgow.
Accepting Mountbatten’s very welcome offer, Morgan nevertheless found that he was “in radical disagreement . . . in many respects” with the syllabus for Rattle that Mountbatten also proposed. A new syllabus was drafted by COSSAC in which time for engagement with senior officers was reduced and time was increased at the end for follow-up staff work.
Overlord would be addressed by the conference in the sequence of its component operational parts: mounting of the operation; assembly and embarkation of forces; cross-Channel voyage; the assault; follow-up and buildup phases; administrative [logistical] aspects of the buildup, including movement and maintenance [supply] problems during this phase; and combined signals organization. Lengthy discussion of the system of command and control or employment of air or airborne forces was to be deferred on grounds that the commanders would determine that for themselves.11
This would be followed by a visit to a nearby Combined Operations training station, HMS Dun Donald, which specialized in beach assault and organization and procedures for integrated communication. Provided would be further explanation of the combined signals organization; landing ships, craft, and amphibians; and mobile radio direction-finding equipment. At Dun Donald participants also would inspect the layout of a headquarters ship. Such ships had proven themselves off North Africa for Torch in 1942, and shortly would do so again in the invasion of Sicily. Headquarters ships would be critical assets for the ground force command staffs on D-Day.
Back at Largs, the conference would conclude with the scope of combined training for the assault phase, proposed combined training cycles, summary of decisions reached during the conference, and more periods as required.12
Difficult to conceal, the gathering for a multiday conference of so many Allied operational commanders, including forty-some general and flag officers, presented a security challenge.13 That was turned to the advantage of COSSAC’s first task of deception and feint, Cockcade. The fact of the Largs conference was used to reinforce a specific deception, Operation Tindall, which was intended to convey to the Germans the false suggestion of active planning for an Anglo-Russian invasion of northern Norway that in part would be mounted from Scotland.14 Conference participation was set, as Morgan recalled, to “include all the principal contestants in our COSSAC scheming as well as the chief leaders of thought from outside our organization.”15 Put another way, they were key skeptics.
The risk of a lengthy discussion of the “strategical problem,” shorthand for the Mediterranean versus cross-Channel debate and a sure touch point for Anglo-American disagreement, worried the planners. To deal with that in advance, Morgan wrote a read-ahead “strategical problem” background paper. There he defined the “strategical problem” exclusively in terms of COSSAC’s mandate from the Combined Chiefs of Staff, elaborated by the Trident agreements.16 For the assembled commanders, the larger strategy debate thus would be taken off the table.
Good plan. Conference Rattle, held from June 28 to July 1, 1943, began, as hoped, with the participants focused only on the challenges of a cross-Channel assault as their “strategical problem.” These alone, however, were of sufficient difficulty to frustrate agreement.
Among many challenges in the proposed operation, greatest concern was expressed for fire support for the assault troops between suspension of air and naval bombardment and the troops’ hitting the beaches and getting their own artillery into action. Arguing from the lessons of their exercises, army participants urged a landing “just before first light.” Naval participants responded that the vast number and array of ships and craft would make organizing the landing in the dark of night “almost an impossible problem.” Landing in daylight would be necessary. Work to resolve this basic issue would continue.17
With agreement on a plan still elusive, Morgan and Mountbatten persevered. Then a glimmer of approval came from one critic. Participants coalesced in support that grew to approach enthusiasm. They fixed on a cross-Channel assault in the vicinity of Caen near the base of the Cotentin Peninsula with some of the landed forces, American, swinging southwest to capture the port of Cherbourg by the fourteenth day after the landing (D+14). Rattle participants concluded from the then-relatively weak local defenses evident at the time that the Germans did not believe the Allies could make a successful assault through the Caen area. Success “would turn upon our surprising them by maintaining larger forces through these beaches than they expected, as a result of efficient beach maintenance [logistical] organization and development of artificial ports.”18
In June 1943, cross-beach efficiency even remotely approaching the scale of Neptune in support of Overlord had not been demonstrated in combat by the Allies. Artificial ports were a new idea. However, exercises to show that required rates of over-the-beach resupply could be achieved had begun in the spring and would continue.19 Field tests of components for artificial ports, which were under way in the harsh weather along the Scottish coast, were building confidence that the Allies indeed could take their ports with them.
One evening from the roof of the hotel, Rattle participants watched the departure of a vast convoy outbound from the Clyde Estuary carrying the First Canadian Infantry Division to the Mediterranean for the invasion of Sicily. Through a talented Women’s Royal Navy Service signaler, First Canadian Army commander Gen. Andrew McNaughton sent a flashing light message to the men in the ships to wish them well in their fight ahead.20
For Canadians, the convoy was a reminder that their country’s five-division, two-brigade overseas army was being split into two widely separated corps by the existence of two competing Allied strategies.21 For all the Rattle participants, the coincidence of the convoy’s departure was sobering. They knew that Operation Husky, the imminent invasion of Sicily, would provide a limited test in combat not just of Allied troops but of many of the weapons, systems, and amphibious assault tactics that would be crucial to the success of a cross-Channel invasion. Before the eyes of these Overlord planners and commanders also sailed tangible evidence of the larger “strategical problem” the conference organizers had sought to set aside so as to focus on coming to grips with the needs of Overlord: the Mediterranean strategy’s continuing competition with the cross-Channel attack for scarce combat resources.
Returning to London, Lord Mountbatten reported on Rattle to the Chiefs of Staff Committee on behalf of COSSAC and Lt. Gen. Jacob Devers, commander of the European Theater of Operations, U.S. Army. With twenty days remaining and new focus on the areas of concern and endorsement from the conference, the COSSAC planners turned with a will to completing the Overlord Outline Plan.22
The men and women of COSSAC always tackled the challenge of a return to the Continent with determination equally matched by spirit. At one point the Army Section made light of the seemingly intractable problems of over-the-beach buildup with a skit satirizing the Navy Section and titled “Operation Overboard.” For security, all copies had to be withdrawn and destroyed quickly.23 Had he met them, Shakespeare would have recognized COSSAC’s “happy few.”24
Their plan was completed in time to meet Morgan’s deadline. Printed on pale green paper and marked “U.S.—Secret British—Most Secret,” the plan endeavored to make the most of the limited forces allotted. Envisioned and illustrated in mostly hand-drawn maps, the units’ nationality were type-distinguished with colored pencil symbols. There were three main landing beaches between Ouistreham in the east and Isigny to the west, two British and one American. On D-Day, each beach would be assaulted by one division. Each assault division would be supported by a brigade-equivalent of tanks. The American division also would be reinforced by a regimental combat team. Covering the flanks and the stretch between the British and American beaches would be units of British Commandos and U.S. Army Rangers. A British airborne division would be dropped in the area surrounding the city of Caen. There would be three smaller insertions of American paratroopers behind the American beach. Hand-drawn was a detailed representation of one of the two artificial harbors to be created. There was an elaborate map of Normandy’s terrain with soil composition color coded as to suitability for tactical airfields.25
The objective of the plan was to strike with forces from the UK on the then-target date of May 1, 1944, to “secure a lodgment on the Continent from which further offensive operations can be developed.” The area of the lodgment was required to have port facilities sufficient to maintain an Allied ground force of twenty-six to thirty divisions and enable augmentation of the force at a rate of three to five divisions per month from the United States and elsewhere.26
The “Digest of Operations” for Overlord gave the reasons why Pas de Calais and Caen-Cotentin areas were most favored by COSSAC’s planners. These included access to beaches that were more sheltered from prevailing winds than those at other sites, a critical factor for getting ashore and expanding and sustaining the force over the beach. In the COSSAC planners’ designation of operational areas, the Pas de Calais was defined to be the area between Gravelines and the River Somme. Caen was the area between the River Orne and the base of Cotentin Peninsula. The Cotentin Peninsula included the port of Cherbourg.
To the planners, the advantages to landing in the Pas de Calais were offset by several concerns. One was the concentration of German fighter aircraft in that area. That was compounded by the assessment that still more of the Luftwaffe could be brought to bear in response to an Allied landing with minimal redeployment from its concentration of fighters to the north to defend against the long-range bombing of Germany.
The need to expand the Pas de Calais beachhead to gain the use of ports would present an unappealing choice: either a push west across many water obstacles to the French Channel ports of Le Harve and Rouen or northeast along the Belgian coast to reach Zeebrugge or even Antwerp, an area also replete with water obstacles.27 These included polders that the Belgians had flooded to good defensive effect against the Germans in World War I.
From its outset, a landing in the Pas de Calais would confront the strongest German beach defenses on the French coast. These could be defeated through “very heavy and sustained bombardment from sea and air.” However, the planners concluded that bombardment would introduce a further negative. The exits heading inland from the beaches would be damaged to an extent that would impede movement to build up Allied forces in the lodgment to exploit the landing.28
Terrain opportunities for expansion of a Pas de Calais lodgment were considered to be poor. They would require military maneuvers that would be unsound “unless the German forces are in a state not far short of final collapse.”29
The COSSAC planners proposed instead a landing in the Caen-Cotentin area on the basis of comparative advantages that had emerged in their studies. They had determined that, like the Allies, the Luftwaffe also would be penalized by the flying distance from their bases to the Caen-Cotentin area. That improved the balance of advantages in favor of Allied versus German air power over the lodgment area. The terrain behind the landing beaches offered better potential for expansion of the lodgment, while avoiding intertwining the lines of supply for different national armies. For that reason Anglo-Canadian forces were assigned to the left flank to push toward Caen and the Americans to the right flank (again, looking from the sea) to push south and then swing west to capture the ports of Cherbourg and Brest.30
In selecting the Caen-Cotentin area over the Pas de Calais, the geography and disposition of Axis forces and beach defenses in France in mid-1943 had led the COSSAC planners to a stratagem that exploited the advent of a new technical capability, artificial ports. As discussed at the Rattle Conference, the stratagem was this:
An attempt has been made to obtain tactical surprise by landing in a lightly defended area—presumably lightly defended as, due to its distance from a major port, the Germans consider a landing there unlikely to be successful. This action, of course, presupposes that we can offset the absence of a port in the initial stages by the provision of improvised sheltered waters. It is believed that this can be accomplished.31
Tactical surprise and concentration of force were the plan’s foundation. Turning the Caen-Cotentin area’s outward operational unattractiveness to Allied advantage enabled surprise. In the planners’ view, “Concentration of the assault forces is considered essential if we are to ensure adequate air support and if our limited assault forces are to avoid defeat in detail.”32
The “Overlord Outline Plan” was recommended as having a “reasonable prospect for success” by the COSSAC planners mindful of, and apprehensive about, the limited resources they had been allocated for the initial assault compared with the operation’s importance and complexity. Their recommendation was made conditional on achievement of three goals: sustaining and expanding the Allied force over the French beaches until a port could be captured; reducing German fighter aircraft forces to the greatest possible extent; and not having more than twelve full-strength, first-rank German divisions in the area on D-Day. Stated in the Outline Plan, Lieutenant General Morgan also emphasized these conditions in his letter of transmission to the COS Committee.
Morgan wrote to the COS that, “in my opinion, it is possible to undertake the operation described, on or about the target date named, with the sea, land, and air forces specified, given a certain set of circumstances in existence at that time.” Dividing these circumstances between those under the Allies’ direct control and those under their indirect control, he first summarized the former. These were foremost the challenge, being addressed, of sustaining the invasion force over the beaches for two to three months until French port facilities could be restored and, second, the need to supply required shipping, naval landing craft, and transport aircraft. From this Morgan concluded that “in view of the limitations in resources imposed by my directive, we may be assured of a reasonable chance of success on 1 May 1944 only if we concentrate our efforts on an assault across the Norman beaches about Bayeux.”33
Morgan’s letter then turned to circumstances only indirectly under Allied control. Morgan cited the need to reduce “as far as it is humanly possible” on land and in the air over France “to the narrowest possible margin” the difference in strength between German forces defending from behind strong fortifications and Allied forces landing on the beaches after a cross-Channel voyage. Noting that considerable capability existed to affect this margin with forces available and growing in the United Kingdom, Morgan concluded that the Allies, nevertheless, were “largely dependent upon events that will take place on other war fronts, principally on the Russian front, between now and the date for the assault.” As a basis for sustained coordination of every Allied effort to this end, Morgan suggested that the COS “adopt the outlook that Operation OVERLORD is even now in progress.”34
In London on July 15, Morgan submitted COSSAC’s draft outline plan for Overlord to the COS Committee in anticipation of the Quadrant Conference. Later that day, Generals Morgan and Barker also would host a visit to COSSAC and brief the “Overlord Outline Plan” to a key American participant, Secretary of War Henry L. Stimson. The timing of that meeting and the conclusions Stimson drew from it would prove critical.