Allied land forces that saw combat in Normandy on D-Day itself came from Canada, the United Kingdom and the United States of America. Free French forces and Poland also participated in the battle after the assault phase, and there were also contingents from Belgium, Czechoslovakia, Greece, the Netherlands, and Norway. Other Allied nations participated in the naval and air forces. Once the beachheads were secured, a three-week military buildup occurred on the beaches before Operation Cobra, the operation to break out from the Normandy beachhead began. The battle for Normandy continued for more than two months, with campaigns to establish a foothold on France, and concluded with the close of the Falaise pocket, the subsequent liberation of Paris on 25 August 1944, and the German retreat across the Seine which was completed on 30 August 1944.
In the East, the vastness of space will… permit a loss of territory… without suffering a mortal blow to Germany’s chance for survival. Not so in the West! If the enemy here succeeds… consequences of staggering proportions will follow within a short time.
The British, under Churchill, wished to avoid the costly frontal assaults of World War I. Churchill and the British staff favoured a course of allowing the insurgency work of the Special Operations Executive to come to widespread fruition, while making a main Allied thrust from the Mediterranean Sea to Vienna and into Germany from the south, concentrating on the weaker Axis ally, Italy. Such an approach was also believed to offer the advantage of creating a barrier to limit the Soviet advance into Europe. However, the U.S. government believed from the onset that the optimum approach was the shortest route to Germany emanating from the strongest Allied power base (ie. Great Britain). They were adamant in their view and made it clear that it was the only option they would support in the long term. Two preliminary proposals were drawn up: Operation Sledgehammer, for an invasion in 1942, and Operation Roundup, for a larger attack in 1943, which was adopted and became Operation Overlord, although it was delayed until 1944.
This operation will be the primary United States and British ground and air effort against the Axis of Europe. Following the establishment of strong Allied forces in France, operations designed to strike at the heart of Germany and to destroy her military forces will be undertaken. We have approved the outline plan for Operation Overlord.
—-Report by Allied Combined Chiefs of Staff, Quebec Conferece, August 1943
In part because of lessons learned by Allied troops in the raid on Dieppe of 19 August 1942, the Allies decided not to assault a French seaport directly in their first landings. The short operating range of British fighters, including the Spitfire and Typhoon, from UK airfields greatly limited the number of potential landing sites, in order to maximise the possibility of air support. Geography reduced the choices further to two sites: the Pas de Calais and the Normandy coast.
Normandy presented serious logistical problems, not the least of which was that the only viable port in the area, Cherbourg, was heavily defended. Many among the higher echelons of command argued that the Pas de Calais would make a more suitable landing area on these grounds alone. Although the Pas de Calais was the shortest distance to the European mainland from the UK, it was the most heavily fortified and defended landing site. Normandy was hence chosen as the landing site.
Landings in force on a broad front in Normandy would permit simultaneous threats against the port of Cherbourg, coastal ports further west in Brittany, and an overland attack towards Paris and towards the border with Germany. Normandy was a less-defended coast and an unexpected but strategic jumping-off point, with the potential to confuse and scatter the German defending forces.
COSSAC plan proposed a landing from the sea by three divisions, with two brigades landed by air. In total, 47 divisions would be committed to the Battle of Normandy: 19 British, five Canadian and one Polish division under overall British command, and 21 American divisions with one Free French division, totalling over a million troops.
In preparation, the BBC appealed for holiday pictures and snaps of France for an exhibition. Those of the Normandy beaches were singled out to create detailed geological maps of the area. What was already known of the make-up was that the targeted beaches were underpinned in places by ancient woodland, which had created peat bogs not far below the beaches surface. Tests on similar beaches in Norfolk in 1943 proved them unsuitable for taking the weight of heavy tanks and transport, so detailed maps of the area were required. In December 1944, Operation Postage Able used an X-craft to collect suitable data for all of the beaches.
On 7 April and 15 May Montgomery presented his strategy for the invasion at St Paul's School. He envisaged a ninety day battle, ending when all the forces reached the Seine, pivoting on an Allied-held Caen, with British and Canadian armies forming a shoulder and the U.S. armies wheeling to the right.
The objective for the first 40 days was to create a lodgement that would include the cities of Caen and Cherbourg (especially Cherbourg, for its deep-water port). Subsequently, there would be a breakout from the lodgement to liberate Brittany and its Atlantic ports, and to advance to a line roughly 125 miles (190 km) to the southwest of Paris, from Le Havre through Le Mans to Tours, so that after ninety days the Allies would control a zone bounded by the rivers Loire in the south and Seine in the northeast.
The Allies developed new technologies for Overlord. The "mulberry," a mobile, prefabricated concrete harbor, allowed the Allies to supply their beachhead without capturing one of the heavily defended Channel ports, as did the Pipe-Line Under The Ocean (PLUTO.)  General Percy Hobart, an unconventional military engineer, assembled a force of modified Sherman and Churchill tanks known as Hobart's Funnies, which were used at Normandy to great effect.
In the months leading up to the invasion, the Allies conducted a deception operation, Operation Bodyguard, designed to persuade the Germans that areas other than northern France would be threatened as well (such as the Balkans and the south of France). Then, in the weeks leading up to the invasion, in order to persuade the Germans that the main invasion would really take place at the Pas de Calais, and to lead them to expect an invasion of Norway, the Allies prepared a massive deception plan, called Operation Fortitude. Operation Fortitude North would lead the Axis to expect an attack on Norway; the much more vital Operation Fortitude South was designed to lead the Germans to expect the main invasion at the Pas de Calais, and to hold back forces to guard against this threat rather than rushing them to Normandy.
An entirely fictitious First U.S. Army Group ("FUSAG"), supposedly located in southeastern Britain under the command of General Lesley J. McNair and General George S. Patton, Jr., was created in German minds by the use of double agents and fake radio traffic. The Germans had an extensive network of agents operating in the UK. Unfortunately for them, every single one had been "turned" by the Allies as part of the Double Cross System, and appropriate agents were dutifully sending back messages "confirming" the existence and location of FUSAG and the Pas de Calais as the likely main attack point. Dummy tanks (some inflatable), trucks, and landing craft, as well as troop camp facades (constructed from scaffolding and canvas) were placed in ports on the eastern and southeastern coasts of Britain, and the Luftwaffe was allowed to photograph them. During this period, most of the Allied naval bombardment was focused on Pas de Calais instead of Normandy. The Allied Forces even went as far as to broadcast static over Axis accessible radioways and convinced Germany to expend efforts to try to decode white noise, further leading Germany away from the upcoming Normandy invasion.
In aid of Operation Fortitude North, Operation Skye was mounted from Scotland using radio traffic, designed to convince German traffic analysts that an invasion would also be mounted into Norway. Against this phantom threat, German units that otherwise could have been moved into France were instead kept in Norway.
Operation Cover (June 2-5) used Eighth Air Force Missions 384,388, 389, & 392 to bomb transportation and airfield targets in Northern France and "coastal defenses, mainly located in the Pas de Calais coastal area, to deceive the enemy as to the sector to be invaded".
The last part of the deception occurred on the night before the invasion: a small group of SAS operators deployed dummy paratroopers over Le Havre and Isigny. These dummies led the Germans to believe that an additional airborne assault had occurred; this tied up reinforcing troops and kept the true situation unclear. On that same night, two RAF squadrons (No. 617 Squadron and No. 218 Squadron) created an illusion of a massive naval convoy sailing for the Cap d'Antifer (15 miles north of Le Havre). This was achieved by the precision dropping of strips of metal foil. The foil caused a radar return mistakenly interpreted by German radar operators as a fleet of small craft towing barrage balloons.
Allied forces rehearsed their roles for D-Day months before the invasion. On 28 April 1944, in south Devon on the British coast, 749 USA soldiers and sailors were killed when German torpedo boats surprised one of these landing exercises, Exercise Tiger.
The effectiveness of the deception operations was increased by a news blackout from Britain. Travel to and from the Irish Free State was banned, and movements within several miles of the coasts restricted. The German embassies and consulates in neutral countries were flooded with all sorts of misleading information, in the well-founded hope that any genuine information on the landings would be ignored with all the confusing chaff.
In the weeks before the invasion it was noticed that the crossword puzzles printed in the British Daily Telegraph newspaper contained a surprisingly large number of words which were codewords relating to the invasion. MI-5 (the Security Service) first thought this was a coincidence, but when the word Mulberry was one of the crossword answers, MI-5 then interviewed the compiler — a schoolmaster Leonard Dawe — and were convinced of his innocence. According to National Geographic, in 1984 a former student of the compiler claimed that he had picked up the words while eavesdropping on soldiers' conversations around the army camps and suggested their use in the puzzles. This assertion has not been independently verified, and Marc Romano, author of the book Crossworld: One Man's Journey into America's Crossword Obsession, gives several reasons why the story is implausible.
There were several leaks prior to or on D-Day. Through the Cicero affair, the Germans obtained documents containing references to Overlord, but these documents lack all detail. Another such leak was Gen. Charles de Gaulle's radio message after D-Day. He, unlike all the other leaders, stated that this invasion was the real invasion. This had the potential to ruin the Allied deceptions Fortitude North and Fortitude South. For example, Eisenhower referred to the landings as the initial invasion. The Germans did not believe de Gaulle and waited too long to move in extra units against the Allies.
The British were to take an airborne assault on the River Orne. The British objective was to secure the Orne River bridges; first to prevent German armor from using them cross the river and disrupt the landings; second to hold them against destruction by the retreating Germans so that they could be used by Allied armor and logistics as the invasion moved inland. The British amphibious assault units would attack through Sword and Gold Beaches. The United States had an airborne division and land units which were to take Omaha beach, Pointe du Hoc and Utah Beaches. The Canadians would team up with British units to attack Sword Beach. Also, the British and Canadians had separate beaches Gold Beach and Juno Beach, respectively.
The Invasion Fleet was drawn from eight different navies comprising warships and submarines, split into the Western Naval Task Force (Rear-Admiral Alan G Kirk) and the Eastern Naval Task Force (Rear-Admiral Sir Philip Vian). The fleet was overall led by Admiral Sir Bertram Ramsay.
The Allies assigned codenames to the various operations involved in the invasion. Overlord was the name assigned to the establishment of a large-scale lodgement on the Continent. The first phase, the establishment of a secure foothold, was codenamed Neptune, according to the D-day museum: The armed forces use codenames to refer to the planning and execution of specific military operations. Operation Overlord was the codename for the Allied invasion of northwest Europe. The assault phase of Operation Overlord was known as Operation Neptune. (...) Operation Neptune began on D-Day (6 June 1944) and ended on 30 June 1944. By this time, the Allies had established a firm foothold in Normandy. Operation Overlord also began on D-Day, and continued until Allied forces crossed the River Seine on 19 August 1944.
Through most of 1942 and 1943, the Germans had rightly regarded the possibility of a successful Allied invasion in the west as remote. Preparations to counter an invasion were limited to the construction, by the Organisation Todt, of impressive fortifications covering the major ports. The number of military forces at the disposal of Nazi Germany reached its peak during 1944 with 59 divisions stationed in France, Belgium and the Netherlands.
In late 1943, the obvious Allied buildup in Britain prompted the German Commander-in-Chief in the west, Field Marshal Gerd von Rundstedt, to request reinforcements. In addition to fresh units, von Rundstedt also received a new subordinate, Field Marshal Erwin Rommel. Rommel originally intended only to make a tour of inspection of the Atlantic Wall. After reporting to Hitler, Rommel requested command of the defenders of northern France, Belgium and the Netherlands. These were organised as Army Group B in February 1944. (The German forces in southern France were designated as Army Group G, under General Johannes Blaskowitz).
Rommel had recognized that for all their propaganda value, the Atlantic Wall fortifications covered only the ports themselves. The beaches between were barely defended, and the Allies could land there and capture the ports from inland. He revitalised the defenders, who laboured to improve the defences of the entire coastline. Steel obstacles were laid at the high-water mark on the beaches, concrete bunkers and pillboxes constructed, and low-lying areas flooded. Given the Allied air supremacy (12,000 Allied aircraft against 300 Luftwaffe fighters), booby-trapped stakes known as Rommelspargel (Rommel's asparagus) were set up on likely landing grounds to deter airborne landings.
These works were not fully completed, especially in the vital Normandy sector, partly because Allied bombing of the French railway system interfered with the movement of the necessary materials, and also because the Germans were convinced by the Allied deception measures and their own preconceptions that the landings would take place in the Pas de Calais, and so they concentrated their efforts there.
The Germans had nevertheless extensively fortified the foreshore area as part of their Atlantic Wall defences (including tank top turrets and extensive barbed wire), believing that any forthcoming landings would be timed for high tide (this caused the landings to be timed for low tide). The sector which was attacked was guarded by four divisions, of which the 352nd and 91st were of high quality. The other defending troops included Germans who were not considered fit for active duty on the Eastern Front (usually for medical reasons) and various other nationalities such as conscripted Poles and former Soviet prisoners-of-war who had agreed to fight for the Germans rather than endure the harsh conditions of German POW camps. These "Ost" units were provided with German leadership to manage them.
Rommel proposed that the armoured formations be deployed close to the invasion beaches. Von Geyr argued that the Panzer formations should be concentrated in a central position around Paris and Rouen, and deployed en masse against the main Allied beachhead when this had been identified. When the matter was brought to Hitler, he gave an unworkable compromise solution, giving three tank divisions to Rommel, and allowing Von Geyr to scatter the other tanks across Northern France and the Netherlands. The other mechanized divisions capable of intervening in Normandy were retained under the direct control of the German Armed Forces HQ (OKW) and were initially denied to Rommel.
A full moon was required both for light for the aircraft pilots and for the spring tide, effectively limiting the window of opportunity for mounting the invasion to only a few days in each month. Eisenhower had tentatively selected 5 June as the date for the assault. However, on 4 June, conditions were clearly unsuitable for a landing; wind and high seas made it impossible to launch landing craft, and low clouds prevented aircraft finding their targets. The Germans meanwhile took comfort from the existing poor conditions and believed an invasion would not be possible for several days. Some troops stood down, and many senior officers were absent. Rommel, for example, decided to leave to attend his wife's birthday observance. At a vital meeting on 5 June, Eisenhower's chief meteorologist James Stagg predicted a slight improvement in the weather for 6 June. This was based on weather reports transmitted from the Captain class frigate HMS Grindall, which, since April, had been on station in mid-Atlantic transmitting weather reports every three hours, day and night. The officer responsible for sending the weather reports was Lieutenant H.R. Curry R.N.V.R. On 4 June, his weather reports indicated a ridge of high pressure behind a deep depression. He forecast that the ridge would move in an easterly direction to reach the south-west approaches late on 5 June and show an improvement in the weather, which up to that point had shown very strong winds, heavy rain and very rough seas, resulting from the passage of a deep depression. On this basis, General Eisenhower, after much consideration, decided to commence the invasion, despite opposition from some of his staff.
You are about to embark upon the Great Crusade, toward which we have striven these many months. The eyes of the world are upon you. The hopes and prayers of liberty-loving people everywhere march with you. In company with our brave Allies and brothers-in-arms on other Fronts, you will bring about the destruction of the German war machine, the elimination of Nazi tyranny over the oppressed peoples of Europe, and security for ourselves in a free world.
To eliminate the enemy's ability to organize and launch counterattacks during the amphibious assault phase, airborne operations were utilized to seize key objectives, such as bridges, road crossings, and terrain features, particularly on the eastern and western flanks of the landing areas. The airborne landings some distance behind the beaches were also intended to ease the egress of the amphibious forces off the beaches, and in some cases to neutralize German coastal defense batteries and more quickly expand the area of the beachhead. The U.S. 82nd and 101st Airborne Divisions were assigned to objectives west of Utah Beach. The British 6th Airborne Division was assigned to similar objectives on the eastern flank. 530 Free French paratroopers from the British Special Air Service Brigade, were assigned to objectives in Brittany from 5 June to August.  (Operation Dingson, operation Samwest).
On Sword Beach, the regular British infantry came ashore with light casualties. They had advanced about 8 kilometres (5 mi) by the end of the day but failed to make some of the deliberately ambitious targets set by Montgomery. In particular, Caen, a major objective, was still in German hands by the end of D-Day, and would remain so until the Battle for Caen, 8 August.
The Canadian forces that landed on Juno Beach faced heavy batteries of machine-gun nests, pillboxes, other concrete fortifications, and a seawall twice the height of the one at Omaha Beach.  Despite the obstacles, the Canadians were off the beach within hours and advancing inland.  The Canadians were the only units to reach their D-Day objectives, although most units fell back a few kilometres to stronger defensive positions.
At Gold Beach, the casualties were also quite heavy, because the Germans had strongly fortified a village on the beach. However, the 50th (Northumbrian) Infantry Division overcame these difficulties and advanced almost to the outskirts of Bayeux by the end of the day. The linkup with commando units securing the Port-en-Bessin gave the Allies a base to deploy their PLUTO pipeline, as an alternative to the experimental 'Tombola', a conventional tanker-ship to shore storage system.
The Americans who landed on Omaha beach faced the veteran German 352nd Infantry Division, one of the best trained on the beaches. Omaha was the most heavily fortified beach, and the majority of landings missed their assigned sectors. Commanders considered abandoning the beachhead, but small units of infantry, often forming ad hoc groups, eventually infiltrated the coastal defenses. Further landings were able to exploit the initial penetrations and by the end of the day two isolated footholds had been established. The tenuous beachhead was expanded over the following days, and the original D-Day objectives were accomplished by D+3.
At Pointe du Hoc, the task for the 2nd Ranger battalion (James Earl Rudder) was to scale the 30 meter (100 ft) cliffs under enemy fire and grenades with ropes and ladders, and then destroy the guns there. The beach fortifications themselves were still vital targets since a single artillery forward observer based there could have called down accurate fire on the U.S. beaches. The Rangers were eventually successful, and captured the fortifications. They then had to fight for 2 days to hold the location, losing more than 60% of their men.
Casualties on Utah Beach, the westernmost landing zone, were the lightest of any beach, with 197 out of the roughly 23,000 troops that landed. Although the 4th Infantry Division troops that landed on the beach found themselves too far to the southeast, they landed on a lightly defended sector that had relatively little German opposition, and the 4th Infantry Division was able to press inland by early afternoon, linking up with the 101st Airborne Division.
Once the beachhead was established, the Mulberry Harbours were made operational around 9 June. One was constructed at Arromanches by British forces, the other at Omaha Beach by American forces. Severe storms on 19 June interrupted the landing of supplies and destroyed the Omaha harbour. However, the Arromanches harbour was able to supply around 9,000 tons of materiel daily until the end of August 1944, by which time the port of Cherbourg had been secured by the Allies.
Despite this, the German 21st Panzer division mounted a concerted counterattack, between Sword and Juno beaches, and succeeded in nearly reaching the channel. Stiff resistance by anti-tank gunners and fear of being cut off caused them to withdraw before the end of 6 June. According to some reports, the sighting of a wave of airborne troops flying over them was instrumental in the decision to retreat.
The Allied invasion plans had called for the capture of Carentan, St. Lô, Caen, and Bayeux on the first day, with all the beaches linked except Utah, and Sword (the last linked with paratroopers) and a front line 10 to 16 kilometres (6–10 mi) from the beaches. In practice none of these had been achieved. However, overall the casualties had not been as heavy as some had feared (around 10,000 compared to the 20,000 Churchill had estimated), and the bridgeheads had withstood the expected counterattacks.
In the western part of the lodgement, U.S. troops were to occupy the Cotentin Peninsula, especially Cherbourg, which would provide the Allies with a deep water harbour. The country behind Utah and Omaha beaches was characterised by bocage; ancient banks and hedgerows, up to three meters (10 ft) thick, spread one to two hundred metres (300–600 ft) apart, both seemingly being impervious to tanks, gunfire, and vision, thus making ideal defensive positions. The U.S. infantry made slow progress, and suffered heavy casualties, as they pressed towards Cherbourg. The airborne troops were called on several times to restart a stalled advance. The far side of the peninsula was reached on 18 June. Hitler prevented German forces from retreating to the strong Atlantic Wall fortifications in Cherbourg, and after initially offering stiff resistance, the Cherbourg commander, Lieutenant General von Schlieben, capitulated on 26 June. Before surrendering however, he had most of the facilities destroyed, making the harbour inoperable until the middle of August.
Whilst the Americans headed for Cherbourg, a unit of troops led by the British moved towards the city of Caen. Believing Caen to be the "crucible" of the battle, Montgomery made it the target of a series of attritional attacks. The first was Operation Perch, which attempted to push south from Bayeux to Villers-Bocage where the armour could then head towards the Orne and envelop Caen, but was halted at the Battle of Villers-Bocage. After a delay owing to the difficulty of supply because of storms from 17 June until 23 June, a German counterattack (which was known through Ultra intelligence) was pre-empted with Operation Epsom. Caen was severely bombed and then occupied north of the River Orne in Operation Charnwood from 7 July until 9 July. A major offensive in the Caen area followed with all three British armoured divisions, codenamed Operation Goodwood from 18 July until 21 July that captured the high ground south of Caen while the remainder of the city was captured by Canadian forces during Operation Atlantic. A further operation, Operation Spring, from 25 July until 28 July, by the Canadians secured limited gains south of the city at a high cost.
An important element of Montgomery's strategy was to cause the Germans to commit their reserves to the eastern part of the theatre to allow an easier breakout from the west. By the end of Goodwood, the Germans had committed the last of their reserve divisions; there were six and a half Panzer divisions facing the British and Canadian forces compared to one and a half facing the United States armies. Operation Cobra was launched on 25 July by the U.S. First Army and was extremely successful with the advance guard of VIII Corps entering Coutances at the western end of the Cotentin Peninsula, on 28 July, after a penetration through the German lines.
On 1 August, VIII Corps became part of Lieutenant General George S. Patton's newly-arrived U.S. Third Army. On 4 August, Montgomery altered the invasion plan by detaching only a corps to occupy Brittany and hem the German troops there into enclaves around the ports, while the rest of the Third Army continued east. The U.S. First Army turned the German front at its western end. Because of the concentration of German forces south of Caen, Montgomery moved the British armour west and launched Operation Bluecoat from 30 July until 7 August to add to the pressure from the United States armies. This drew the German forces to the west, allowing the launch of Operation Totalize south from Caen on 7 August.
By the beginning of August, more German reserves became available with the realisation that no landings were going to take place near Calais. The German forces were being encircled, and the German High Command wanted these reserves to help an orderly retreat to the Seine. However, they were overruled by Hitler who demanded an attack at Mortain at the western end of the pocket on 7 August. The attack was repelled by the Allies, who again had advance warning from Ultra. The original Allied plan was for a wide encirclement as far as the Loire valley, but Bradley realized that many of the German forces in Normandy were not capable of maneuver by this stage, and he obtained Montgomery's agreement by telephone on 8 August for a "short hook" further north to encircle German forces. This was left to Patton to effect, moving nearly unopposed through Normandy via Le Mans, and then back north again towards Alençon. The Germans were left in a pocket with its jaws near Chambois. Fierce German defense and the diversion of some American troops for a thrust by Patton towards the Seine at Mantes prevented the jaws closing until 21 August, trapping 50,000 German troops. Whether this could have been achieved earlier with more prisoners taken has been a matter of some controversy. Patton's thrust prevented the Germans from establishing the Seine as a defensive line, and the Canadian First and British Second Armies both advanced there, bringing the war in Normandy in their sector to a close and meeting the projected schedule set by Montgomery earlier than expected.
Operations continued in the British and Canadian sector until the end of the month. On 25 August, the 2nd U.S. Armored Division fought its way into Elbeuf, making contact with both British and Canadian armoured divisions there. The 2nd Canadian Infantry Division advanced into the Foret de la Londe, a heavily forested area where German troops inflicted great loss on French troops in the siege of Paris in 1870-71, on the morning of 27 August. The area was strongly held and the 4th and 6th Canadian brigades sustained heavy casualties over the course of three days as the Germans fought a delaying action in terrain well-suited to the defense. The Germans pulled back on the 29th, withdrawing completely over the Seine on the 30th.
On the afternoon of the 30th the 3rd Canadian Infantry Division crossed the Seine near Elbeuf and entered Rouen to a jubilant welcome.
The appointment of Bernard Montgomery was questioned by some[who?] Americans, who would have preferred the urbane Harold Alexander to have commanded the land forces. Montgomery, in turn, had doubts about the appointment of Dwight D. Eisenhower. In the end, however, Montgomery and Eisenhower cooperated to excellent effect in Normandy; their well-known disagreements came much later.
The campaign in Normandy is considered by historians to end either at midnight on 24 July 1944 (the start of Operation Cobra on the American front), 25 August 1944 (the liberation of Paris), or 30 August 1944, the date the last German unit retreated across the River Seine. The original Overlord plan anticipated a ninety-day campaign in Normandy with the ultimate goal of reaching the Seine; this goal was met early. American forces were fighting in Brittany as anticipated by General Montgomery during the latter weeks of the campaign, and their historians consider the Normandy campaign to have ended with the massive breakout of Operation Cobra.
The U.S. official history describes the fighting beginning on 25 July as the "Northern France" campaign, and includes the fighting to close the Falaise Gap, which the British/Canadians/Poles consider to be part of the Battle of Normandy. Volume II of the Official History of the Canadian Army in the Second World War by C.P. Stacey, published in 1955, as well as the Canadian Army's official Historical Summary of the Second World War, published in 1948, define the Battle of Normandy as lasting from 6 June 1944 to 1 September 1944.
SHAEF and the governments were very nervous of stagnation, and there were reports of Eisenhower requesting Montgomery's replacement in July. The lack of forward progress is often attributed to the nature of the terrain in which much of the post-landing fighting in the U.S. and parts of the British sectors took place, the bocage (small farm fields separated by high earth banks covered in dense shrubbery, well suited for defence), as well as the usual difficulties of opposed landings. However, as at the battle of El Alamein, Montgomery kept to his original attritional strategy, reaching the objectives within his original ninety day target.
Victory in Normandy was followed by a pursuit to the French border in short order, and Germany was forced once again to reinforce the Western Front with manpower and resources from the Soviet and Italian fronts.
By September, Allied forces of seven field armies (two of which came through southern France in Operation Dragoon) were approaching the German frontier. Allied material weight told heavily in Normandy, as did intelligence and deception plans. The general Allied concept of the battle was sound, drawing on the strengths of both Britain and the United States. German dispositions and leadership were often faulty, despite a credible showing on the ground by many German units. In larger context the Normandy landings helped the Soviets on the Eastern front, who were facing the bulk of the German forces and, to a certain extent, contributed to the shortening of the conflict there.
Allied logistics, intelligence, morale and air powerEdit
Victory in Normandy stemmed from several factors. The Allies ensured material superiority at the critical point (concentration of force) and logistical innovations like the PLUTO pipelines and Mulberry harbours enhanced the flow of troops, equipment, and essentials such as fuel and ammunition. Movement of cargo over the open beaches exceeded Allied planners' expectations, even after the destruction of the U.S. Mulberry in the channel storm in mid-June. By the end of July 1944, one million American, British, Canadian, French, and Polish troops, hundreds of thousands of vehicles, and adequate supplies in most categories were ashore in Normandy. Although there was a shortage of artillery ammunition, at no time were the Allies critically short of any necessity. This was a remarkable achievement considering they did not hold a port until Cherbourg fell. By the time of the breakout the Allies also enjoyed a considerable superiority in numbers of troops (approximately 3.5:1) and armored vehicles (approximately 4:1) which helped overcome the natural advantages the terrain gave to the German defenders.
Allied intelligence and counterintelligence efforts were successful beyond expectations. The Operation Fortitude deception plan before the invasion kept German attention focused on the Pas-de-Calais, and indeed high-quality German forces were kept in this area, away from Normandy, until July. Prior to the invasion, few German reconnaissance flights took place over Britain, and those that did saw only the dummy staging areas. Ultra decrypts of German communications had been helpful as well, exposing German dispositions and revealing their plans such as the Mortain counterattack.
German commanders at all levels failed to react to the assault phase in a timely manner. Communication problems exacerbated the difficulties caused by Allied air and naval firepower. Local commanders also seemed unequal to the task of fighting an aggressive defence on the beach, as Rommel envisioned. The German High Command remained fixated on the Calais area, and von Rundstedt was not permitted to commit the armored reserve. When it was finally released late in the day, success was immeasurably more difficult, and even the 21st Panzer Division, which was able to counterattack earlier, was stymied by strong opposition that had been allowed to build at the beaches. Overall, despite considerable Allied material superiority, the Germans kept the Allies bottled up in a small bridgehead for nearly two months, aided immeasureably by terrain factors.
Although there were several well-known disputes among the Allied commanders, their tactics and strategy were essentially determined by agreement between the main commanders. By contrast, the German leaders were bullied and their decisions interfered with by Hitler, controlling the battle from a distance with little knowledge of local conditions. Field Marshals von Rundstedt and Rommel repeatedly asked Hitler for more discretion but were refused. Von Rundstedt was removed from his command on 29 June after he bluntly told the Chief of Staff at Hitler's Armed Forces HQ (Field Marshal Keitel) to "Make peace, you idiots!" Rommel was severely injured by Allied aircraft on 16 July. Field Marshal von Kluge, who took over the posts held by both von Rundstedt and Rommel, was compromised by his association with some of the military plotters against Hitler, and he would not disobey or argue with Hitler for fear of arrest. As a result, the German armies in Normandy were placed in deadly peril by Hitler's insistence on counterattack rather than retreat after the American breakthrough. Kluge was relieved of command on 15 August and took his own life shortly afterwards. The more independent Field Marshal Walter Model took over when the Germans in Normandy were already in the midst of defeat.
The German commanders also suffered in the quality of the available troops. 60,000 of the 850,000 under Rundstedt's command were prisoners of war captured on the Eastern Front. These Ost units had volunteered to fight against Stalin, but when instead used to defend France against the Western Allies, ended up being unreliable. Many surrendered or deserted at the first available opportunity.
The cost of the Normandy campaign had been high for both sides. From D-Day to 21 August the Allies had landed 2,052,299 men in northern France. The Allies lost around 209,672 casualties from June 6 to the end of August, around 10 % of the forces landed in France. The casualties breaks down to 36,976 killed, 153,475 wounded and 19,221 missing. Split between the Army-Groups; the Anglo-Canadian Army-Group suffered 16,138 killed, 58,594 wounded and 9,093 missing for a total of 83,825 casualties. The American Army-Group suffered 20,838 killed, 94,881 wounded and 10,128 missing for a total of 125,847 casualties. To these casualties it should be added that no fewer than 4,101 aircraft were lost and 16,714 airmen were killed in direct connection to Operation Overlord. Thus total Allied casualties rises to 226,386 men.
78 Free French SAS (Special Air Service) were killed and another 195 wounded from 6 June to the beginning of August in Brittany. For Allied tank losses there are no direct number. Estimations are that around 4,000 tanks were destroyed, of which 2,000 were fighting in American units.
The German casualties remains unclear.  The estimates of the German casualties stretches from 288,000 men to 450,000 men. Just in the Falaise Gap the Germans lost around 60,000 men in killed, wounded and captured. The majority of the German casualties consisted of POWs as nearly 200,000 were captured during the closure of the battle. The Germans committed around 2,300 tanks and assault guns to the battle in Normandy, and only around 100 to 120 were brought back across the Seine.[nb 6] The overwhelming majority of the German tanks destroyed were put out of action by the Allied airforce, while very few of the Allied tank losses were inflicted by the Luftwaffe.
19,860 French civilians were killed during the liberation of Normandy, and an even greater number were wounded. The number excludes the 15,000 civilians killed and the 19,000 wounded in the bombings of Normandy in preparation of the invasion from January to June of 1944. As many as 70,000 French civilians may have been killed during the liberation of France in 1944.  Many cities and towns in Normandy and northern France were totally devastated by the fighting and the bombings. In Caen, there was at the end of the battle 8,000 livable quarters for a population of over 60,000. 
The landings were planned to take place in May 1944, but poor weather conditions and insufficient buildup delayed the landings until June. By then, the Allies had taken Rome in the Italian Campaign, and in the Pacific War, the Americans were launching their first strikes on Japan. On the Eastern Front, the Red Army were planning their own offensive, Operation Bagration, to drive the Germans away from Soviet territory. Combined with the Allied lodgement established at Normandy, the second front in Western Europe that had been demanded by Stalin since the Tehran Conference had been established, the Axis powers were driven back from all fronts.
The Normandy campaign has drawn criticism in grand strategy in that it diverted resources and units from other theatres (such as the Italian and Pacific fronts) for the invasion. The Italian front had ceased to be an effective front after the Normandy campaign, and the Pacific front experienced manpower shortages for the Leyte and Okinawa campaigns. The quick successes of Operation Dragoon compared with Normandy also lent criticism to the execution of the Normandy campaign. However, the Normandy front was hindered by Hitler's attempts to hold the West at any cost. As the Allies were closing in on Paris and sealing the Falaise Gap, an invasion in southern France was also launched. Hitler was eager to hold on to the Belgian and northern French coasts as bases for the "V" weapons, which had started launching against the UK. The linkup with the southern French forces occurred on 12 September as part of the drive to the Siegfried Line.
The Normandy landings not only signalled the beginning of the end for Nazi Germany, it heralded in the start of the race for Europe, which some historians consider to be the start of the Cold War (see Origins of the Cold War).
The beaches of Normandy are still known by their invasion codenames today. Streets near the beaches are still named after the units that fought there, and occasional markers commemorate notable incidents. At significant points, such as Pointe du Hoc and Pegasus Bridge, there are plaques, memorials or small museums. The Mulberry harbour still sits in the sea at Arromanches. In Sainte-Mère-Église, a dummy paratrooper hangs from the church spire.
↑Zetterling, p. 32: "On 25 July there were 812,000 US soldiers and 640,000 British in Normandy."
↑Zetterling, p. 341: "By 21 August, the Allies had landed 2,052,299 men in Normandy."
↑Zetterling, p. 32: "When Operation Cobra was launched, the Germans had brought to Normandy about 410,000 men in divisions and non-divisional combat units. If this is multiplied by 1.19 we arrive at approximately 490,000 soldiers. However, until 23 July, casualties amounted to 116,863, while only 10,078 replacements had arrived."
↑Tamelander, M, Zetterling, N (2004), Avgörandes Ögonblick: Invasionen i Normandie. Norstedts Förlag, p. 341. To these numbers should also be added the losses of the allied airforces operating. The allied airforces made 480,317 takeoffs in direct connection to the operation with the loss of no fewer than 4,101 planes and the lives of 16,696 crewmen.
↑Tamelander, M, Zetterling, N (2004), Avgörandes Ögonblick: Invasionen i Normandie. Norstedts Förlag, p. 341. To these numbers should also be added the losses of the allied airforces operating. The allied airforces made 480,317 takeoffs in direct connection to the operation with the loss of no fewer than 4,101 planes and the lives of 16,696 crewmen. Thus total Allied casualties rises to 226,386 men.
↑Tamelander, M, Zetterling, N (2004), Avgörandes Ögonblick: Invasionen i Normandie. Norstedts Förlag, p. 342. Approximately 4000 Allied tanks was destroyed, of which 2000 were fighting in American units.
↑Montgomery wrote of his intent to tie down German armoured forces near Caen in a policy directive on 30 June 1944: "My broad policy, once we had secured a firm lodgement area, has always been to draw the main enemy forces in to the battle on our eastern flank, and to fight them there, so that our affairs on the western flank could proceed the easier." See C.P. Stacey, The Canadian Army 1939-45: A Historical Summary, p.195
↑Both publications are available online from the Directorate of History and Heritage, a department of the Department of National Defence, as free downloads. The definition of the Battle of Normandy is also evident in another publication by the Army's Historical Section entitled Canada's Battle in Normandy.
↑Keegan, John (1982). Six Armies in Normandy. Penguin Books. p. 61. ISBN 0 14 00.5293.
↑Tamelander, M, Zetterling, N (2004), Avgörandes Ögonblick: Invasionen i Normandie. Norstedts Förlag, p. 341.
↑Tamelander, M, Zetterling, N (2004), Avgörandes Ögonblick: Invasionen i Normandie. Norstedts Förlag, p. 341.
↑Corta, Henry, (1921-1998), a Free French SAS lieutenant veteran, (1952) : les bérets rouges (red berets)
↑ Corta, Henry, (1997) : Qui ose gagne (Who dares wins)
↑Tamelander, M, Zetterling, N (2004), Avgörandes Ögonblick: Invasionen i Normandie. Norstedts Förlag, p. 342.
↑Tamelander, M, Zetterling, N (2004), Avgörandes Ögonblick: Invasionen i Normandie. Norstedts Förlag, p. 342.
↑Tamelander, M, Zetterling, N (2004), Avgörandes Ögonblick: Invasionen i Normandie. Norstedts Förlag, p. 342.
↑Tamelander, M, Zetterling, N (2004), Avgörandes Ögonblick: Invasionen i Normandie. Norstedts Förlag, p. 342.
↑Beevor, A (2009), D-Day: The Battle for Normandy. Historiska Media, p. 555.
↑Beevor, A (2009), D-Day: The Battle for Normandy. Historiska Media, p. 556.
↑Gilbert, Martin (1989). Second World War. pp. 531, 540, 544.
↑The World at War, episode 13. 1974. Event occurs at 29:50-31:58.
↑"…the manpower available to the US Army in the Pacific and to the Marine Corps had been limited by the war in Europe" Keegan, John (1989). The Second World War. London: Pimlico. p. 467. ISBN 9-780712-673488.
↑Keegan, John (1989). The Second World War. pp. 362–363.
Morning: Normandy Invasion (June–August 1944), episode 17 of the 1974 ITV series The World at War narrated by Laurence Olivier features an extensive coverage of the Allied preparations and the actual events.
Battlefield-The Battle for Normandy, 100 minute 1994 documentary that compares Allied and German commanders, personnel, equipment, and tactics before, during, and after the battle.
Ken Burns-The War, a seven-part PBS documentary series about World War II as seen through the eyes of men and women from four quintessentially American towns.
Soldiers: Heroes of WWII. The German campaign of the game, titled "Hunter", takes place after the invasion of D-Day and has the player in control of German tank commander Michael Wittmann.
1944 D-Day Operation Overlord, a complete simulation of the entire Battle of Normandy. Players have the option to be a pilot, a sailor, a tank commander, or any other person who was fighting for either army.
Atlantic Wall, a large 1970s American boardwargame by SPI depicting the battle from the landings through to the breakout, at company and battalion level, and using a similar game system to Wacht Am Rhein. Due to be reprinted in 2008.
Cobra, a 1970s American boardwargame by SPI depicting the breakout and Falaise Pocket, at brigade and division level (with Tiger tank battalions). Reprinted by TSR, Inc in the late 1980s with an extra map covering the initial landings.