10 key Second World War dates you need to know

The Second World War started on 1 September 1939 and ended on 2 September 1945. But what are the other key dates from those decades that marked the conflict? From epic battles to atomic bombs, Professor Jeremy Black rounds up 10 of the most significant WW2 dates...

A mushroom cloud over Nagasaki, Japan

7 July 1937: Clash near the Marco Polo Bridge, close to Beijing

The triggering of the full-scale war with China that lasted until 1945 began with an obscure clash involving a Japanese unit on night manoeuvres near the Marco Polo Bridge southwest of Beijing on the night of 7–8 July 1937. The Japanese felt the nation’s honour had been challenged and sent fresh forces to the region. Hardliners in the Japanese army used the incident to press for a settlement of China on their terms, while the Chinese nationalist leader, Jiang Jieshi, was unwilling to propriate Japan. As a result, an intractable struggle began that greatly weakened both sides. Large-scale conflict broke out toward the end of July, and Beijing was occupied on 29 July.


10 May 1940: Germans launch offensive in the West

The German unwillingness to limit their war to the conquest of Poland and to launch meaningful peace talks meant that the Second World War broadened out. Hitler was eager to profit from the ability Poland’s defeat offered for Germany to fight on only one front and argued that Germany enjoyed a window of opportunity thanks to being more prepared for war than Britain or France.

Bad weather in the severe winter of 1939–40, caution on the part of the German High Command, and the need for preparations, delayed the attack until May 1940. On 10 May, the Germans attacked Belgium and the Netherlands, both hitherto neutral, and invaded France. They successfully gained and used the initiative, while the French and British suffered from a failure to prepare for fluid defence in depth.

Germany’s success in its subsequent seven-week campaign transformed the strategic situation in Europe. Victory led Hitler to a conviction of his own ineluctable success, and that of the Wehrmacht under his leadership. Thanks to this victory, the Germans would clearly be able to fight on, and any successful challenge to them would now have to overcome German dominance of Western Europe.


12 August 1940: Battle of Britain begins

The first concerted attack on British airfields was launched on 12 August 1940. The fall of France ensured that German airbases were now close to Britain. The Luftwaffe (German air force) was instructed to help prepare the way for invasion by driving British warships from the Channel. However, Luftwaffe commanders were increasingly concerned to attack the RAF and its supporting infrastructure in order to prepare the way for reducing Britain to submission by a bombing war on civilian targets – a strategy that would put the Luftwaffe centre-stage.

The first major military campaign in history to be fought entirely in the air, the Battle of Britain saw the Luftwaffe launch a large-scale attack against Britain’s air defences. Yet by October 1940, the RAF was victorious. The lack of clarity in the relationship between air attack and invasion affected German strategy, but there was also a lack of preparation for a strategic air offensive, notably in aircraft, pilots, tactics and doctrine. British fighting quality proved a key element in the German defeat, as did the support provided by radar and the ground-control organisation.

The Battle Of Britain, A Heinkel He 111 bomber flying over the Isle of Dogs in the East End of London, at at the start of the Luftwaffe's evening raids of 7 September 1940, 7 September 1940. (Photo by German Air Force photographer/ IWM via Getty Images)
The Battle of Britain: a Heinkel He 111 bomber flies over the Isle of Dogs in the East End of London at the start of the Luftwaffe’s evening raids of 7 September 1940. (Photo by German Air Force photographer/ IWM via Getty Images)

22 June 1941: Launching of Operation Barbarossa

Hitler’s overconfidence and contempt for other political systems reinforced his belief that Germany had to conquer the Soviet Union in order to fulfill her destiny and obtain Lebensraum (living space). He was convinced that a clash with Communism was inevitable, and was concerned about Stalin’s intentions. Hitler was confident that the Soviet system would collapse rapidly, and he was happy to accept misleading intelligence assessments of the size and mobilisation potential of the Red Army. He believed that the defeat of the Soviet Union would make Britain ready to settle and to accept German dominance of Europe.

On 22 June, 151 German divisions, supported by 14 Finnish and 13 Romanian divisions – nearly 3.6 million German and allied troops, backed by 3,350 tanks and 1,950 aircraft – were launched in a surprise attack. There was no realistic political plan to accompany the strategy. The failure to knock the Soviet Union out that year left the Germans involved in an intractable struggle that was to lead to eventual defeat


7 December 1941: Attack on Pearl Harbor

The Japanese attack on the United States meant the conflict was clearly a world war. Japan could have restricted itself to attacking the British and Dutch colonies in South-East Asia, but, instead chose to also attack America in order to prevent it from opposing Japanese expansion. This led to a surprise attack on the base of the American Pacific Fleet at Pearl Harbor on the island of Oahu in the Hawaiian archipelago.

The Japanese planned to wreck the American Pacific Fleet. It was a classic case of an operational-tactical success, but a strategic failure. Some 353 aircraft from six Japanese carriers totally destroyed two American battleships and damaged five more, while, in an attack on the naval air station at Kaneohe Bay, nearly 300 American aircraft were destroyed or damaged on the ground.

The attack, however, revealed grave deficiencies in Japanese (and American) planning, as well as in the Japanese war machine. Only 45 per cent of naval air requirements had been met by the start of the war, and the last torpedoes employed in the attack were delivered only two days before the fleet sailed.

The damage to America’s battleships (some of which were salvaged and used anew) forced an important shift in American naval planning toward an emphasis on their carriers, the Lexington, the Yorktown and the Enterprise, which, despite Japanese expectations, were not in Pearl Harbor when it was attacked.

No attack on this scale was to be launched on any other fleet during the war. Because of the focus on destroying warships rather than strategic assets, there was no third-wave attack on the fuel and other harbour installations. Had the oil farms (stores) been destroyed, the Pacific Fleet would probably have had to fall back to its Californian base at San Diego, gravely hindering American operations in the Pacific.

Furthermore, the course of the war was to reveal that the strategic concepts that underlay the Japanese plan had been gravely flawed. Aside from underrating American economic strength and the resolve of its people, the Japanese had embarked on an attack that was not essential. Their fleet was larger than the American Pacific and Asiatic Fleets especially in carriers, battleships and cruisers, and the American fleets, as a result, were not in a position to have prevented the Japanese from overrunning British and Dutch colonies, which was their major expansionist goal.

Possible controversy over the lack of the necessary American preparedness at Pearl Harbor was largely put aside in response to the shock of the Japanese surprise attack. The devastating nature of the incident encouraged a rallying round the American government.

Pearl Harbor: sailors stand amid wreckage watching as the USS Shaw explodes in the centre background. (Photo by Fox Photos/Getty Images)
Pearl Harbor: sailors stand amid wreckage watching as the USS Shaw explodes in the centre background. (Photo by Fox Photos/Getty Images)



4 June 1942: Battle of Midway

The continued capacity of the American navy, however, was shown clearly, on 4 June, with the American victory in the battle of Midway, a naval-air battle of unprecedented scale. This battle also reflected the superiority of American repair efforts and intelligence. So also did the combination of fighter support with carriers (in defence) and of fighters and bombers (in attack) was crucial.

The Americans encountered serious problems in the battle, and contingency and chance played a major role in it, but at Midway and, increasingly, more generally, the Americans handled the uncertainty of war far better than the Japanese. The Japanese navy, which had doctored its war games for Midway, was affected by the tension between two goals: those of decisive naval battle and of the capture of Midway Island. This ensured that the Japanese had to decide whether to prepare their aircraft for land or ship targets – an issue that caused crucial delay during the battle.

While the American ability to learn hard-won lessons from the earlier battle of the Coral Sea (4–8 May 1942) was highly significant, the dependence of operations on tactical adroitness and chance played a major role in a battle in which the ability to locate the target was crucial. An American strike from the Hornet aircraft carrier failed with the fighters and dive-bombers unable to locate the Japanese carriers. Lacking any, or adequate, fighter support, torpedo-bomber attacks suffered very heavy losses.

However, the result of these attacks was that the Japanese fighters were unable to respond,to the arrival of the American dive-bombers – a fortuitous instance of coordination. In only a few minutes, in a triumph of dive bombing, three carriers were wrecked, a fourth following later; once wrecked, they sunk.

These minutes shifted the arithmetic of carrier power in the Pacific. Although their aircrews mostly survived, the loss of 110 pilots was especially serious as the Japanese had stressed the value of training and had produced an elite force of aviators. The Japanese looked upon a carrier and its combat aircraft as an inseparable unit, with the aircraft as the ship’s armaments much like guns on fighting surface craft. Once lost, the pilots proved difficult to replace, not least because of a shortage of fuel for training. More seriously, the loss of four carriers’ maintenance crews could not be made up.

Smoking hulk of the Japanese heavy cruiser Mikuma, which was destroyed during the battle of Midway. (Photo by Time Life Pictures/US Navy/The LIFE Picture Collection via Getty Images)
Smoking hulk of the Japanese heavy cruiser Mikuma, which was destroyed during the battle of Midway. (Photo by Time Life Pictures/US Navy/The LIFE Picture Collection via Getty Images)

The Americans won decisively in the carrier battle, the Japanese losing all four of their heavy carriers present, as well as many aircraft. There was no opportunity for the Japanese to use their battleships, as the American carriers prudently retired before their approach, while the American battleships had already been sent to the West Coast.

This was one of the respects in which Midway was no Tsushima (a major naval battle fought between Russia and Japan during the Russo-Japanese War; a Japanese victory). The inflexible conviction of Isoroku Yamamoto (Japanese Marshal Admiral and commander-in-chief of the Combined Fleet) of the value of battleships in any battle with the Americans had served him ill. This poor judgment ensured that the Japanese had lost their large-scale offensive capacity at sea, at least as far as carriers were concerned. Conversely, the American admirals may have acted differently had they had battleships at their disposal.

American carrier strategy was in part a ‘lack-of-battleship’ strategy. The battle ensured that the Congressional elections on 3 November 1942 took place against a more benign background than if earlier in the year.



5 July 1943: Germans launch battle of Kursk

The last major German offensive on the Eastern Front sought to exploit the opportunities provided by a major German salient. They sought to break through the flanks of the salient and to achieve an encirclement triumph to match the Soviet success at Stalingrad the previous winter.

Still engaging in strategic wishful thinking, Hitler saw this as a battle of annihilation in which superior will would prevail. He hoped that victory would undermine the Allied coalition, by lessening western confidence in the likelihood of Soviet victory and increasing Soviet demands for a second front in France.

The Germans were outnumbered by the Soviets who had prepared a defence system that thwarted the German tank offensive. After heavy losses and only modest gains, Hitler cancelled the operation that had cost him much strength. Having stopped the Germans, the Soviets were now in a position to counterattack. The Germans were now to be driven back in a near-continuous process.



6 June 1944: D-Day

The Allied landings in northern France – known as D-Day – began on 6 June 1944. American, British and Canadian forces landed in Normandy, as Operation Neptune (the landings) paved the way for Operation Overlord (the invasion). Under the overall command of Eisenhower, the Allies benefited from well-organised and effective naval support for the invasion and from air superiority. In addition, a successful deception exercise, Operation Fortitude, ensured that the Normandy landing was a surprise.

The Germans had concentrated more of their defences and forces in the Calais region, which offered a shorter sea crossing and a shorter route to Germany. Normandy, in contrast, was easier to reach from the invasion ports on the south coast of England, especially Plymouth, Portland and Portsmouth. The Germans lacked adequate naval and air forces to contest an invasion, and much of their army in France was of indifferent quality, short of transport and training, and, in many cases, equipment.

German commanders were divided about where the attack was likely to fall and about how best to respond to it. They were particularly split over whether to move their ten panzer divisions close to the coast, so that the Allies could be attacked before they could consolidate their position, or to mass them as a strategic reserve. The eventual decision was for the panzer divisions, whose impact greatly worried Allied planners, to remain inland, but their ability to act as a strategic reserve was lessened by the decision not to mass them and by Allied air power. This decision reflected the tensions and uncertainties of the German command structure.

The fate of the landings was very varied. Specialised tanks developed by the British to attack coastal defences – for example, Crab flail tanks for use against minefields – proved effective in the British sector: Gold, Juno and Sword beaches. The Canadian and British forces that landed on these beaches also benefited from careful planning and preparation, from the seizure of crucial covering positions by airborne troops, and from German hesitation about how best to respond.

The situation was less happy on Omaha beach. The Americans there were inadequately prepared in the face of a good defence, not least because of poor planning and confusion in the landing, including the launching of assault craft and Duplex Drive (amphibious) Sherman tanks too far offshore, as well as a refusal to use the specialised tanks. The Americans sustained about 3,000 casualties, both in landing and on the beach, from positions on the cliffs that had not been suppressed by air attack or naval bombardment. Air power could not deliver the promised quantities of ordnance on target and on time.

Troops from the 48th Royal Marines at Saint-Aubin-sur-mer on Juno Beach, Normandy, France, during the D-Day landings, 6 June 1944. (Photo by Hulton Archive/Getty Images)
Troops from the 48th Royal Marines at Saint-Aubin-sur-mer on Juno Beach, Normandy, France, during the D-Day landings, 6 June 1944. (Photo by Hulton Archive/Getty Images)

Eventually the Americans were able to move inland, but, at the end of D-Day, the bridgehead was shallow and the troops in the sector were fortunate that the Germans had no armour to mount a response. This owed much to a failure in German command that reflected rigidities stemming from Hitler’s interventions.

Military writer JFC Fuller pointed out that Overlord marked a major advance in amphibious operations as there was no need to capture a port in order to land, reinforce and support the invasion force. He wrote in the Sunday Pictorial of 1 October 1944:

“had our sea power remained what it had been, solely a weapon to command the sea, the garrison Germany established in France almost certainly would have proved sufficient. It was a change in the conception of naval power which sealed the doom of that great fortress. Hitherto in all overseas invasions the invading forces had been fitted to ships. Now ships were fitted to the invading forces… how to land the invading forces in battle order… this difficulty has been overcome by building various types of special landing boats and pre-fabricated landing stages.”

To Fuller, this matched the tank in putting the defence at a disadvantage. The Dieppe operation had shown that attacking a port destroyed it; thus the need to bring two prefabricated harbours composed of floating piers with the invasion. In 1944, the Germans still, mistakenly, anticipated that the Allies would focus on seizing ports.

The laying of oil pipelines under the Channel was also an impressive engineering achievement that contributed to the infrastructure of the invasion. The experience gained in earlier landings was important, although the scale of the operation and the severity of the resistance on the landing beaches were greater than in North Africa and Italy.

It proved difficult for the Allies to break out of Normandy, although they succeeded in doing so in August and were able then to advance on the German frontier. This was not a process in which amphibious operations played a role until in the autumn efforts were made to clear the Scheldt estuary. It was the same the following year. The emphasis was on advances overland and not on amphibious attacks – for example in northern Holland or north-western Germany. The situation therefore was very different to that in the Pacific.


23–26 October 1944: Battle of Leyte Gulf

The Americans used their naval and air superiority, already strong and rapidly growing, to mount a reconquest of the Philippines from October 1944. That operation helped ensure a naval battle: that of Leyte Gulf of 23–26 October, the largest naval battle of the war and one (or rather a series of engagements) that secured American maritime superiority in the western Pacific.

The availability of oil helped determine Japanese naval dispositions and, with carrier formations based in home waters and the battle force based just south of Singapore, any American movement against the Philippines presented a very serious problem for Japan. There was growing pessimism in Japan and losing honourably became a goal for at least some Japanese naval leaders. The head of the Naval Operations Section asked on 18 October 1944 that the fleet be afforded “a fitting place to die” and “the chance to bloom as flowers of death”.

With Operation Sho-Go (Victory Operation) the Japanese sought to intervene by luring the American carrier fleet away, employing their own carriers as bait, and then using two naval striking forces (under Vice-Admirals Kurita and Kiyohide respectively) to attack the vulnerable American landing fleet. This overly complex scheme posed serious problems for the ability of American admirals to read the battle and control the tempo of the battle, and, as at Midway, for their Japanese counterparts in following the plan.

In a crisis for the American operation, one of the strike forces was able to approach the landing area and was superior to the American warships. However, instead of persisting, the strike force retired; its exhausted commander, Kurita, lacking knowledge of the local situation, not least due to the difficulties of identifying enemy surface ships. The net effect of the battle was the loss of four Japanese carriers, three battleships including the Musashi, 10 cruisers, other warships and many aircraft.


9 August 1945: Dropping of second atom bomb, on Nagasaki

This made more of an impact than the first bomb, dropped on Hiroshima on 6 August 1945. It now seemed likely that the Americans could mount an inexorable process of bombing. As a result, Japan agreed to surrender unconditionally. An Imperial broadcast on 15 August announced the end of hostilities. It followed Emperor Hirohito’s intervention at the Imperial Conference on 9 and 14 August.

The limited American ability to deploy more bombs speedily was not appreciated. Some 6.7 square kilometres of Nagasaki was reduced to ashes; 73,884 people were killed and 74,909 injured. Long-term health consequences were calamitous.

Jeremy Black is a professor of history at the University of Exeter who specialises in British and continental European history. His publications include The Age of Total War, 1860–1945 (Praeger Publishers Inc, 2006) and World War Two: A Military History (Routledge, 2003)


This article was first published by HistoryExtra in 2016