The largest and most ambitious military expedition in history was the invasion of Normandy in northern France by British, American and Canadian forces that took place in the summer of 1944. Even nature played a role. It took more than a year for military planners to orchestrate ( 精心策划 ) every movement to open up a second front in Europe. This would liberate France and way for the final assault ( 攻击 ) on Germany itself. Everything was controlled, that is, except the weather. D- day, the code name given to the day of invasion, was originally scheduled for 5 June 1944. This date had been arrived at by considering two factors--moonlight and tide. With the arrival of 5 June, the weather was so bad that General Eisenhower, supreme commander of the invasion forces, was forced to postpone the invasion by one day. When he met with his staff to review their options, they were faced with the cruel reality that 6 June did not look much better than the original D-Day. The meteorological (气象的) report gave a thin ray of hope that a lull (平息) in the storm would allow enough time to launch the invasion. Finally, Eisenhower made his decision. "I am quite positive we must give the order," he said. "I don't like it, but there it is. I don't see how we can do anything else." Within hours, an armada of 3,000 landing craft, 2,500 other ships, and 500 naval vessels began to leave English ports. Meanwhile, critical errors by the German side allowed them to be taken completely by surprise. Due to the bad weather, the German navy canceled its usual patrol of the English Channel. Also, a practice drill scheduled for June 6 was called off. The German meteorological services were unaware of the break in the weather. On the eve of the attack, many of the top German leaders were absent from their commands. The airborne attack became confused because of stiff winds and the evasive flying of the transport planes when they encountered anti-aircraft fire. As a result, the paratroopers were scattered over a wide area and most missed their drop zones, some by as much as 20 miles. The naval bombardment began around 5:45 a.m. The air attack followed. Weather conditions had improved, but they were not perfect. Because of poor visibility caused by low cloud cover, it was decided that the bombers would delay the release of bombs 30 seconds to avoid hitting the assaulting troops. As a result, the bombs fell inland and missed their targets. Although the naval bombardment was more accurate, it was not much more effective against the hardened German gun emplacements.