When the Allied forces landed on the beaches of Normandy early on the morning of 6 June 1944, they launched the most massive military undertaking of World War II. Since then those beaches have borne the code names Utah, Omaha, Gold, Juno, and Sword, the components of Operation Overlord, which is popularly known as D-day. The landings set the stage for the beginning of the end of German occupation of France. The operation was both enormous and complex. Counting combat troops and personnel involved in administrative and logistical support, between 2.6 and 2.7 million individuals participated.
Published print, video, and filmed material on the events of the spring and summer of 1944 proliferated in Great Britain, France, and the United States before and after the fiftieth anniversary of D-day. The focus of this article is the crucial role of weather and tides, physical-geographic factors fundamental to the choice of the invasion date.
Situated between Brittany and the western part of the Paris Basin, the Normandy peninsula is rimmed by sand or pebble beaches backed by cliffs that give way to a pastoral landscape of farms and villages. Irregular hills are separated by marshland and several small rivers. Scattered forests contain mixed stands of oak, chestnut, and beech. The countryside is a patchwork of old earthworks and hedgerows, known locally as bocage, that protect livestock and crops from the bone-chilling Atlantic winds. A characteristic landscape west of Rouen, bocage is an irregular patchwork of low trees and thick, high hedges alternating with small fields or meadows and pastures. Much of the fighting took place in the bocage. These hedges, four to five feet high and almost as thick, were capable of stopping a tank, and frequently did, until an American soldier hit on the idea of attaching steel blades on the front of his tank to uproot the tangled vegetation.
Fields contain corn, buckwheat, and barley, and pastures are covered with wildflowers in the spring. Fruit orchards abound; apples yield the regional specialties -- cider and Calvados. Seaweed and kelp are gathered to use as fertilizer on the local farms, which are underlain by rocky soil. The soils are thin, comprising sand, limestone, marl, chalk, and, in places, flint. Although the interior exhibits some upwarping, the coasts are somewhat lower but rimmed with steep, eroded cliffs, especially in the eastern portion.
The location of Normandy, both as a gateway to the continent and an exit from the European mainland to the British Isles, has seemed to invite military incursions throughout history. The D-day operations were the most recent of actions that are rooted in antiquity. In 1940 Germany overran France with frightening rapidity. The need for a cross-channel invasion to liberate France was recognized, and Prime Minister Winston Churchill noted in the fall of 1941 that it would occur when the tide turned more strongly in favor of the Allies. Stalin had been urging the opening of a second front soon after Germany invaded the Soviet Union. In January 1943, at the Casablanca conference, a committee was formed to devise a plan for Operation Overlord, the code name chosen for what was to become the Normandy landings.
In 1944 what was probably the most ambitious amphibious invasion of modern times was launched in Normandy. Success or failure of the operation hinged on suitable weather conditions. Thus selecting the date of the assault required the talents of the most skilled meteorologists available. The 1942 landings in North Africa provided some lessons for a large-scale amphibious operation. The problem there, as for Normandy, concerned the limitations of long-range forecasting. A universally accepted technique to predict weather accurately for more than one or two days did not, and does not, exist. American meteorologists had been working on five-day forecasts, but the British had found such forecasts to be of little value. …