In July 1943, the Americans and British executed Operation Husky, the invasion of Sicily. It was the first major opposed amphibious landing since Gallipoli in World War I, a seven-division amphibious assault echelon that made it the largest such assault in modern history. The Allies met weak resistance which soon caused the Axis forces to evacuate the island.
Operation Husky is frequently cited as a prelude to the Normandy invasion. As one writer notes, "Sicily was essential for Normandy: a real-life live-fire training exercise [in which lessons were learned] in planning and executing amphibious operations, and in joint and combined organization, planning, and command and control." (1) Among the lessons was the role of planning branches and sequels. Sadly, failure in this step turned the operation into a hollow triumph.
As Joint Publication 3-0, Doctrine for Joint Operations, states, "Many [operational plans] require adjustment beyond the initial stages of the operation. Commanders build flexibility into their plans to preserve freedom of action in rapidly changing conditions." Usually such changes are made through branches and sequels. The former are "options built into the basic plan" and the latter are "subsequent operations based on the possible outcomes of the current operation--victory, defeat, or stalemate." Allied planning for Sicily omitted details beyond the operation. According to Liddell Hart, "The decision to land in Sicily [was] unaccompanied by any conclusion as to further aims." (2)
The United States and Britain discussed two basic courses of action at the Casablanca Conference in January 1943. They included avoiding land combat with Axis forces or invading Sardinia, Sicily, Italy, Greece, or the Dodecanese Islands. Even General George Marshall, Chief of Staff, U.S. Army, supported the idea of avoiding contact with the enemy to prepare for Operation Roundup, but the heads of state rejected the proposal. The British favored actions in the Balkans, but the Americans feared that such a step would delay a cross channel invasion. No one believed that the Allies were strong enough to invade Italy, so the options narrowed to Sardinia and Sicily.
Sicily had several advantages. Its capture would make the Mediterranean safe for shipping, engage and destroy a greater number of German divisions, capture more and better airfields within bombing range of southern Italy, and perhaps cause the Italian government to seek peace. A Sicily operation would satisfy the United States because it would save shipping, employ troops already in theater, and conclude the Mediterranean campaign. In fact, the Americans accepted Sicily largely because it seemed a dead end. These considerations would facilitate the true U.S. objective--cross-channel invasion. The British agreed to Sicily for shipping considerations, a desire to punish Italy, and hope of eliminating Italy from the war. The loss of Sicily would weaken the enemy. (3)
In actuality, the logic for attacking Sicily is best described as a rationale. Operation Husky was not planned within the context of leading to an overarching strategic objective. At Casablanca the Allies chose Sicily not because of anything inherent to Sicily but because, as Samuel Morrison concludes, "Something had to be done in the European theater in 1943," and "it was entered upon as an end unto itself; not as a springboard for Italy or anywhere else." (4) The choice "was a strategic compromise conceived in dissension and born of uneasy alliance--a child of conflicting concepts and unclear in purpose." (5) There was no operational sequel planned after Sicily.
Part of the reason for this omission was that it had been a difficult process just to agree on Sicily. The participants in the Casablanca Conference did not want to tackle what to do next. As Liddell Hart puts it, "An attempt to decide on the next objective would have revived divergencies of view--but in such matters tactful deferment is apt to result in strategic unreadiness. …