US thought a short route would be a more optimum approach for long term.
Operation Sledgehammer and Operation Roundup were the two preliminary proposals drawn up. Operation Sledgehammer was planned to invade Germany in 1942 and Operation Roundup was planned for a larger attack in 1943, which later on became Operation Overload and was delayed until 1944.
In 1943 the then Chief of Staff to the Supreme Allied Commander (COSSAC) British Lieutenant-General Sir Frederick Morgan planned the initial process and later his plan was adopted and refined in the year 1944 by General Dwight David Eisenhower who was the head of the Supreme Headquarters, Allied Expeditionary Force (SHAEF).
Because of the short operating range of the allied fighters made it the ground situation more difficult since limited possibility of amphibious landing sites. The geography reduced the optional striking sites to two: the Pas de Calais and the Normandy coast. Pas de Calais was heavily fortified and defended by the Germans because they know that it offers the shortest path to the European mainland from UK and more importantly it offers a direct route to Germany. Therefore Normandy became an obvious choice for the allied forces to attack.
In January 1944 general Sir Bernard Montgomery was appointed as commander of 21st Army Group to which all the invaing ground forces command was given. He was also responsible for developing the invasion plan. COSSAC proposed a plan to attack with three divisions by sea and two brigades landed by air. Later Montgomery increased the scale of intial attack to five divisions by sea and three by air. In total 47 divisions under the supervision of British command was formulated to the battle of Normandy. The 47 divisions include 21 American, 19 British, 5 Canadian, 1 Polish and 1 Free French division. The total number of troops of aliied forces were 140,000.
Montgomery planned it to be a ninety day battle where British and Canadian forces forming a shoulder and US army moving to the right. Around 6,900 vessels, 4,100 landing craft and 12,000 aircraft would be involved in the invasion. About 10,000 tons of bombs were supposed to be dropped and 14,000 attack sorties had to be flown.
Allied forces rehearsed every day for the D-Day invasion in advance. They don't wanted to take any chances so they rehearsed their to perection.
Germans fortified the the foreshore which was guared by four divisions. The fotification was part of their Atlantic Aall defences and was guarded by the four divisions of which only one division (352nd) was of high quality and that too the cadre of the 321st division-the core of 352nd. The 352nd division has many troops that participated in war against the allied forces before and was carrying out anti-invasion exercises. The other troops include were, usually for medical reasons, and were declared unfit for active duty. After witnessing the harsh reality that prevailed in German POW camps Soviet prisoners agreed to fight for Germans.
Field Marshall Erwin Rommel was given command of the Atlantic Wall. After inspecting the Atlantic Wall Rommel requested Hitler to increase the defences. After inspection he found that Atlantic Wall only covered the ports themselves, beaches were barely defended and there was every possibility of Allies capturing the key points from inland. He improved the defences acrss the coast line and made it stronger. Steel obstacles were laid, booby traps were prepared, bunkers and pillboxes were constructed. Though