After gaining valuable experience in amphibious assaults and inland fighting, Allied planners returned to the plans to invade Northern France, now postponed to 1944. Under the direction of General Dwight D. Eisenhower (Supreme Commander Allied Expeditionary Force) and Frederick Morgan, plans for the invasion of France coalesced as Operation Overlord. With an initial target date of 1 May 1944, the infantry attack was conceived as a joint assault by five divisions transported by landing craft, constituting the largest amphibious operation in military history. The attack was later scheduled for Monday, 5 June 1944, and Normandy was selected for the landing sites, with a zone of operations extending from the Cotentin Peninsula to Caen. There were originally seventeen sectors along the Normandy coastline with codenames taken from one of the spelling alphabets of the time, from Able, west of Omaha, to Rodger on the east flank of the invasion area. Eight further sectors were added when the planned invasion was extended to include Utah on the Cotentin Peninsula. Sectors were further subdivided into beaches identified by the colours Green, Red and White. Operation Overlord called for the British Second Army to assault between the River Orne and Port en Bessin, capture Caen, and form a front line from Caumont-l'Éventé to the south-east of Caen, to acquire airfields and protect the left flank of the United States First Army while it captured Cherbourg. Possession of Caen and its surroundings would give Second Army a suitable staging area for a push south to capture the city of Falaise, which could then be used as a pivot for a swing left to advance on Argentan, the Touques River and then towards the River Seine.