From Citizendium, the Citizens' Compendium
In contingency planning for the European Theater of Operations in World War II, the Chief of Staff, Supreme Allied Commander (COSSAC) had prepared three variants (Cases A-C) of Operation RANKIN. RANKIN was defined as a sudden change in the strength and determination of Germany. In hindsight, these have become classic studies of contingency planning for dealing with unexpected ends of wars. An appropriate version of RANKIN Case C, for example, could have been very useful when the army of Iraq collapsed in the Iraq War; the airborne variant of Operation ECLIPSE airborne case, planned by a different headquarters but with some comparable goals, might also have been a model. In the military literature, these have been discussed as conceptual starting points for scenarios including a government collapse or a coup d'etat.
Cases A and B dealt with situations in which the Germans still fought, but weakened considerably. The requirement, therefore, was to land on the continent as quickly as possible, and defeat Germany from there. Case C dealt with a cessation of resistance, so the aim was to occupy as rapidly as possible appropriate areas from which to take steps to enforce the terms of unconditional surrender laid down by the allied governments.
While the actual plans speak of Operation OVERLORD, this article substitutes the more accurate term Operation NEPTUNE. NEPTUNE was the more tightly held code word for the Normandy invasions, while OVERLORD was a general term for operations in Western Europe, which indeed would include an invasion, in 1944. To some extent, RANKIN replaced earlier concepts in the set of BOLERO-SLEDGEHAMMER-ROUNDUP plans that conceived of a 1943 operation. While the British rejected this overall concept as premature without Mediterranean operations and strategic bombing, a variant of ROUNDUP had been considered as a contingency "quick" invasion.
Operation ECLIPSE was a plan generated by a lower-level headquarters, the First Allied Airborne Army, that dealt with a later and different scenario: a need to take sudden control of Berlin in the event of a collapse of the top government. It was overtaken by events, since it was conceived just before the Rhine was crossed at Remagen Bridge and large forces moved into Germany,
RANKIN Case A
Case A dealt with the situation of "substantial weakening of the strength and morale of the German armed forces" to the extent that a successful assault could be made by Anglo-American forces before the planned major invasion of Western Europe.
If this took place before the end of 1943, no action was feasible unless it was clear Germany was close to collapse, and substantial naval resources were available. If the contingency took place after January 1944, the resources building up for OVERLORD could be used against weak opposition, and, after March, against stronger resistance. It was judged feasible to carry out Case A after January 1944, against the Cotentin Peninsula rather than Normandy, as long as the port of Cherbourg could be seized within 48 hours. Diversionary invasions might be needed in the Pas de Calais and in Southern France; this was essentially a modified OVERLORD.
RANKIN Case B
This dealt with the contingency of German withdrawal from occupied countries, most likely Norway and France. Western FRANCE and NORWAY. "In this case, it was necessary, for political as well as strategic reasons, to occupy the areas vacated, but it was important that the main forces of the Allies should not thereby be tied down far from the eventual centre of action."
Different actions would be required for the two areas. For Norway, the goal would be establishing air and radar bases to protect the supply route to the Soviet Union, and to block German breakouts from the Baltic sea. This could be done with one brigade in northern Norway and one division in southern Norwa.
If Germany withdrew from France, it would probably begin in Bordeaux and the Western ports, with the Pas de Calais the last area to be evacuated. One brigade each was assumed needed for Bordeaux, Brest and Nantes, to prepare them from reinforcements coming directly from the United States. The main Forcible entry at Cherbourg would be by U.S. troops while British troop[s would take Havre and Rouen.
"From these bases, the Allies would establish a line along the SOMME from which to press North-Eastwards through the PAS DE CALAIS to BELGIUM, opening up ports as they proceeded and establishing airfields from which the advance could be covered and the attack on GERMANY itself concentrated. At the same time, MEDITERRANEAN forces would be required to occupy MARSEILLES and TOULON, and to move Northwards thence in LYONS and VICHY."
RANKIN Case C
Case C dealt with possibilities such as a sudden surrender, or at least cessation of organized resistance. Had the Unconditional Surrender policy not been in effect and the July 20 plot succeeded, Case C might have been very relevant. It still could have applied if the plotters did surrender, perhaps with understandings about some authority.
The Case targeted the initial areas to come under control as the Jutland Peninsulal; the ports of Bremen, Hamburg and Kiel; and the large towns of the Ruhr and Rhine Valleys. Using these as bases, the Allies would then occupy the entire Rhine and Ruhr Valleys, and move into Denmark, Schleswig and Holstein. Air bases in these areas would be sufficient to establish air supremacy while disarming the rest og Germany.
In parallel, selected ports on the European coast would be opened, and the capital cities of the occupied countries brought under control. Similar processes would be carried out in Norway and the Mediterranean.
"It was estimated that 24 divisions would be required for the primary areas of occupation: 7 for DENMARK and North-West GERMANY, 6 for the RUHR and 11 for the RHINE valley. Other troops—non-field force formations wherever possible—would be required in support of the various national contingents charged primarily with the rehabilitation of their respective liberated countries."
Operation ECLIPSE airborne case
The RANKIN series was replaced by the ECLIPSE plans issued by Supreme Headquarters, and were the overall approach to the occupation of Germany.
A subset, developed by Lewis Brereton's First Allied Airborne Army staff, ECLIPSE was outside the top-level planning that produced RANKIN and BOLERO-SLEDGEHAMMER-ROUNDUP, but was of interest for a time. Churchill and Montgomery felt it should receive attention, while Eisenhower did not see military need.  Once the surprise crossing of the Rhine was made at Remagen Bridge and large forces poured into Germany, with a decision that the Soviets would take Berlin, ECLIPSE was overtaken by events.
A successful assassination of Hitler, with a struggle over authority, would have been the ideal opportunity for ECLIPSE. There have been several accounts of this plan, involving two to five divisions. In one basic scenario, following heavy bombing, Allied airborne divisions would drop on Berlin's airports:
- 82nd Airborne Division: Templehof and subsidiary Rangsdorf field
- 101st Airborne Division: Gatow and subsidiary Staaken field
- 1st Airborne Division (UK), Special Air Service, (with SAS and 1st Polish Parachute Brigade): Tegel and Oranienberg
To facilitate the linkup to the Berlin units above, a brigade consisting of elements from UK 6th Airborne and 17th Airborne was to drop over the Rhine near Wesel to support Montgomery's crossing. This proposal held the UK 52nd Air Landing Division in reserve
The proposals recognized the reality of limited air transport. Another variant had the initial drops in battalion and regiment strength, not full divisions on major targets.  McKenzie said two regiments from the 82nd and 101st would take Tempelhof, while British paratroopers would drop, in battalion strength, on critical areas in Berlin. The remainder of the five U.K. and U.S. airborne divisions would airland at a secure Templehof, and hold until ground forces could link with them.
- ↑ Forrest E. Pogue, CHAPTER V: Planning Before SHAEF, U.S. Army in World War II, European Theater of Operations, vol. The Supreme Command
- ↑ Historical Sub-Section, Office of Secretary, General Staff (May 1944), History of COSSAC (Chief of Staff to Supreme Allied Commander) 1943-1944, Supreme Headquarters, Allied Expeditionary Force, p. 5
- ↑ Ray S. Cline, Chapter IX: Case History: Drafting the BOLERO Plan, U.S. Army in World War II, The War Department, vol. Washington Command Post: The Operations Division
- ↑ History of COSSAC, p. 24
- ↑ History of COSSAC, p. 25
- ↑ Earl F. Ziemke (1990), CHAPTER XI: Getting Ready for "The Day", Eclipse Plans, The U.S. Army in the Occupation of Germany 1944-1946, Center of Military History, United States Army, p. 163
- ↑ 82nd Airborne during World War II
- ↑ Cornelius Ryan, A Bridge Too Far (need exact ref); also http://forum.axishistory.com/viewtopic.php?f=12&t=39855
- ↑ John McKenzie, “On Time, On Target: The World War II Memoir of a Paratrooper in the 82nd Airborne” , p. 156, quoted at http://forum.axishistory.com/viewtopic.php?f=12&t=39855