The Invasion of Normandy (also known as Operation Overlord[N 1], and widely known as D-Day) was the invasion by and establishment of Western Allied forces in Normandy, during Operation Overlord in 1944 during World War II; the largest amphibious invasion to ever take place.
D-Day, the day of the initial assaults, was Tuesday 6 June 1944. Allied land forces that saw combat in Normandy on that day came from Canada, the Free French forces, the United Kingdom, and the United States. In the weeks following the invasion, Polish forces also participated, as well as contingents from Belgium, Czechoslovakia, Greece, and the Netherlands. Most of the above countries also provided air and naval support, as did the Royal Australian Air Force, the Royal New Zealand Air Force, and the Royal Norwegian Navy.
The Normandy invasion began with overnight parachute and glider landings, massive air attacks and naval bombardments. In the early morning, amphibious landings on five beaches codenamed Juno, Gold, Omaha, Utah, and Sword began and during the evening the remaining elements of the parachute divisions landed. Land forces used on D-Day deployed from bases along the south coast of England, the most important of these being Portsmouth.
The initial plan for Overlord had been completed in time for Winston Churchill to hand a copy to 'Monty' for evaluation, while the two men spent Christmas 1943 at Marakesh. Monty rejected this initial plan, on the grounds that the assault force was too small and the landing area was too narrow, and submitted a revised plan of his own, which was ultimately accepted.  A decoy invasion was also devised in planning to confuse the German defenders, who were expecting an invasion further to the west and were therefore less prepared for the actual invasion point. Planning also went into organizing the various countries involved in the invasion, the paratroopers deployed the night before, and also instructing French resistance fighters to further disrupt and confuse the German troops.
Prior to the landings, a paratrooper force was deployed behind enemy lines to sabotage and disrupt enemy communications.[N 2] The ground invasion began on June 6,[N 3] 1944 at 6:30AM British double summer time, and the full establishment of allied forces occurred on the 25th of August that same year. There were five different landing areas that were to be taken by Allied forces. These areas were to be taken by different allied countries and were codenamed Juno (Canada), Sword (Great Britain), Omaha (US), Utah (US), Gold (Great Britain) with Omaha being the bloodiest and highest casualty inducing.
British and Canadian forces were under the command of General Montgomery, with American forces commanded by Dwight D. Eisenhower. German forces were to be under the control of Rommel, but he was in Berlin at the time visiting his wife. Although he tried to regroup troops to reinforce the defenders he was too late, and instead began massing troops and armor for a counterattack. This lack of leadership hindered the Germans further in their defense.
Entering the Mainland
More Info: Elastic Defense
The battle was an difficult fight for the Allies because the German defenses were quite well built. The beaches housed large amounts of mines, tank traps, barbed wire and many other deterrents. There was also many pillboxes and reinforced structures overlooking perceived landing sights which housed a variety of weapons such as machine guns and artillery. These defences have been under construction for years, as such a landing has been expected, and combined with the natural defences already present, such as beaches and cliffs, made the landing a formidable challenge. Despite this, within hours, a beach head had been established on nearly all of the beaches, with the allies pushing inland. By the end of the day, due to the brave work of American rangers, (and Germany's inferior ability to get supplies to her soldiers) even the bloodbath that had been Omaha beach was well under control of the Allies. The Atlantic Wall had been breached. 
The brutality and iconic nature of the battle has given the battle many spots in the entertainment industry with multiple films such as the popular Saving Private Ryan and being used as a battlefield in video games.
- ↑ Technically, The codename Overlord applied solely to the land forces element of the invasion; the naval forces element was known as Operation Neptune
- ↑ This included a deception effort known as Operation Titanic, which consisted of dummy paratroopers being dropped over a wide area.
- ↑ The invasion had originally been was set for the 5th, but delayed due to weather complications
- ↑ Falconer, Johnathon. D-Day Operations Manual. Haynes Publishing. 2013. ISBN 978 0 85733 234 9 Page 9
- ↑ Williams, Jeffery. The Long Left Flank: The Hard Fought Way to the Reich, 1944-1945. Cooper (1988)
- ↑ The Norwegian Navy in the Second World War
- ↑ Makins, Clifford. High Command. Dragon's Dream. 1981. ISBN 90 6332 851 6.
- ↑ Falconer, Johnathon. Pages 31-32
- ↑ https://www.google.com/amp/amp.history.com/news/landing-at-normandy-the-5-beaches-of-d-day
- ↑ "The Great Crusade" by the extra credits team, ten minutes https://www.google.com/url?sa=t&source=web&rct=j&url=https://m.youtube.com/watch%3Fv%3D-KY1pDLulF4&ved=0ahUKEwiIyNeLnbLaAhUjZN8KHc7RAYAQyCkIJzAA&usg=AOvVaw3VUC2jTg2r2m5_Dgu1fbu7