page_title: Operation Overlord
section_title: Rehearsals and security
hierarchical_section_title: Operation Overlord / Preparations for D-Day / Rehearsals and security
caption_attribution_description: Invasion Training in England - Training with live ammunition
context_page_description: Operation Overlord was the codename for the Battle of Normandy, the Allied operation that launched the successful invasion of German-occupied Western Europe during World War II. The operation was launched on 6 June 1944 with the Normandy landings. A 1,200-plane airborne assault preceded an amphibious assault involving more than 5,000 vessels. Nearly 160,000 troops crossed the English Channel on 6 June, and more than two million Allied troops were in France by the end of August.
  The decision to undertake a cross-channel invasion in 1944 was taken at the Trident Conference in Washington in May 1943. General Dwight D. Eisenhower was appointed commander of Supreme Headquarters Allied Expeditionary Force, and General Bernard Montgomery was named as commander of the 21st Army Group, which comprised all the land forces involved in the invasion. The coast of Normandy of northwestern France was chosen as the site of the invasion, with the Americans assigned to land at sectors codenamed Utah and Omaha, the British at Sword and Gold, and the Canadians at Juno.
context_section_description: Training exercises for the Overlord landings took place as early as July 1943. As the nearby beach resembled the planned Normandy landing-site, the town of Slapton in Devon, was evacuated in December 1943, and taken over by the armed forces as a site for training exercises that included the use of landing craft and the management of beach obstacles. A friendly fire incident there on 27 April 1944 resulted in as many as 450 deaths. The following day, an additional estimated 749 American soldiers and sailors died when German torpedo-boats surprised members of Assault Force "U" conducting Exercise Tiger. Exercises with landing craft and live ammunition also took place at the Combined Training Centre in Inveraray in Scotland. Naval exercises took place in Northern Ireland, and medical teams in London and elsewhere rehearsed how they would handle the expected waves of casualties. Paratroopers conducted exercises, including a huge demonstration drop on 23 March 1944 observed by Churchill, Eisenhower, and other top officials.
  Allied planners considered tactical surprise to be a necessary element of the plan for the landings. Information on the exact date and location of the landings was provided only to the topmost levels of the armed forces. Men were sealed into their marshalling areas at the end of May, with no further communication with the outside world. Troops were briefed using maps that were correct in every detail except for the place names, and most were not told their actual destination until they were already at sea. A news blackout in Britain increased the effectiveness of the deception operations. Travel to and from the Republic of Ireland was banned, and movement within several kilometres of the coast of England restricted.
caption: Training exercise with live ammunition
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