During a few short weeks in the summer of 1940, the Germans defeated France and drove the British from Dunkirk. Hitler had quickly accomplished what the Kaiser had failed to do in four years of attritional fighting during 1914-18. With their main ally defeated and war strategy in ruins, the British found themselves alone and threatened with invasion.
When Adolf Hitler came to power in 1933 he promised to reverse the terms of the Treaty of Versailles (1919) and reassert Germany's dominance of Europe. Rearmament began almost immediately and the German army, navy and air force expanded.
Seeking to reverse the territorial losses after the First World War, his troops re-occupied the Rhineland in 1936. In March 1938 German troops entered Austria to carry out the Anschluss (unification) of the two German-speaking countries. The French and British governments did nothing to stop these actions.
In 1938, Hitler demanded that the German-speaking part of Czechoslovakia, the Sudetenland, be annexed to Germany. Fearful of a war for which they were unprepared, Britain and France adopted a policy of 'Appeasement'. They agreed to a deal with Germany at Munich in September 1938, brokered by the Italian dictator Mussolini. The Sudetenland was occupied by Germany, and shortly afterwards the whole of Czechoslovakia was seized.
Finally accepting that Germany could not be appeased Britain and France stepped up their rearmament programmes and gave guarantees to Poland, Hitler's next target.
After signing a non-aggression pact with the Soviets, Hitler demanded territorial concessions from the Poles. These were refused and the Germans attacked on 1 September 1939. Britain and France declared war two days later. The Second World War had begun.
On the outbreak of war in 1939 the British Army comprised 50 regular and Territorial divisions. Many of these troops were stationed throughout the world. Over 50,000 soldiers were based in India and garrisons east of Suez.
The British Expeditionary Force (BEF) that was dispatched to France in 1939 consisted of only ten divisions. This force was relatively small compared with those of other combatants. But in addition to their own Army, the British could draw on additional divisions from Australia, Canada, South Africa, West Africa, East Africa and New Zealand. There were also around 200,000 men of the Indian Army stationed on the Indian sub-continent.
During the 1920s and 1930s British and French strategic concepts had stagnated. The generals expected to fight a future war in which defence rather than attack would dominate. They believed that set-piece battles would develop slowly and be dominated by infantry and artillery. They put their faith in the Maginot Line, France's fortified border with Germany. Ignoring the lessons learnt during the battles of 1918, tanks and aircraft were largely cast in a supporting role.
German strategic thinking contrasted greatly with that of the Allies. The Germans emphasised speed of decision-making, speed of manoeuvre and decentralised action by armoured units with motorised infantry and air support. They went to war with fewer tanks than the Allies, but concentrated them in powerful armoured formations rather than dispersing them.
Although there were Allied officers who realised that a new form of warfare was possible, no sustained effort had been made to apply these doctrines in a similar way to that of the German High Command.
The British Expeditionary Force (BEF), commanded by General Lord Gort VC, began arriving in France on 9 September 1939. It spent the next seven months training through a bitter winter in readiness for action. By May 1940 it had been built up to 394,000 men. This consisted of five regular and five Territorial divisions stationed on the Belgian frontier where, as in 1914, the main German attack was expected.
Confident in the strength of the Maginot Line, a series of strong forts guarding the German frontier, the Allies were happy to remain on the defensive. Apart from a very limited advance in the Saar area, they largely restricted themselves to dropping propaganda leaflets on the German civilian population.
Rather than giving direct military assistance to Poland, they put their faith in a policy of economic blockade that would slowly wear Germany down. This period was later nicknamed 'the phoney war'.
On 9 April 1940, Germany invaded Norway in order to secure its iron-ore supplies. Hitler also wanted to use Norway as a base for naval operations against the Allies. The country was quickly overrun, the Germans using their airpower and paratroopers to secure key centres, and defeat the weak Norwegian forces.
British and French troops then landed in the centre and north of the country around Narvik, Aandalsnes and Namsos, but were too few in number and poorly equipped to resist the Germans. By the beginning of June the position was hopeless and Anglo-French forces were evacuated.
On 10 May 1940, the Germans invaded the Netherlands, Belgium and Luxembourg. Using the 'Blitzkrieg' techniques of fast moving armoured formations supported by ground-attack aircraft, mobile artillery and mechanised infantry, they quickly overwhelmed the Dutch and Belgian armies. The Germans seized the initiative from the outset, capturing the key Belgian fort of Eban Emael with a daring airborne operation.
The British and French forces had moved into Belgium to meet the attack. However, the main German effort was directed further south. General Gerd von Runstedt's Army Group A, with 38 infantry and seven armoured divisions advanced through the forests of the Ardennes, considered impassable by the Allies.
Although many French units fought bravely there was little to stop the Germans. The best Allied formations were engaged in Belgium and there was no centrally placed strategic reserve to respond to the new threat.
German tanks crossed the River Meuse at Sedan on 13 May 1940, outflanking the Maginot Line. Breaking through the weak French forces there they raced towards the channel coast, reaching Abbeville on 19 May and cutting off the Allied troops in Belgium.
On the same day an improvised counter-attack southwards by British armour temporarily halted the 7th Panzer Division at Arras. But on 26 May, with the Germans pressing northwards and with Belgian resistance collapsing, General Lord Gort was ordered to evacuate what he could of the British Expeditionary Force (BEF) through Dunkirk.
By 3 June 1940, instead of the 45,000 originally hoped for, 328,000 Allied troops had been taken off the Dunkirk beaches and shipped back to England. This was partly due to the efforts of the Royal Navy and hundreds of civilian ships that had crossed the Channel. It was also due to dogged rearguard actions at Boulogne, Calais and elsewhere, which bought time. The BEF also benefited from Hitler's order on 24 May that his tanks should halt at a time when the German 1st Panzer Division was only 24 kilometres (15 miles) from Dunkirk.
On 5 June 1940, the Germans launched a new offensive from their positions on the Somme. After two days of fierce fighting, they broke through toward Rouen and on 9 June they crossed the Seine. The same day, the Germans attacked on the Aisne and eventually swung towards Switzerland, cutting off the thousands of soldiers still holding the Maginot Line.
The 51st (Highland) Division, which had not been trapped at Dunkirk with the rest of the BEF, was surrounded at St Valéry-en-Caux in Normandy and surrendered on 12 June. The next day Paris was declared an open city. Eight days later a new French government under Marshall Philippe Pétain sued for peace.
Hitler's failure to completely destroy the BEF allowed the nucleus of an army to be saved at Dunkirk. A further 140,000 Allied troops were brought out through Cherbourg and Brest. Nevertheless, the BEF had suffered 68,000 casualties. Most of its equipment, including 64,000 vehicles, 20,000 motorcycles and 2,500 guns, was lost. Britain had lost her main ally and now stood alone.
In a little under seven weeks, at a cost of only 156,000 casualties, Germany had conquered the Netherlands, Belgium and France and ejected the British from Western Europe. It would be four long years before they returned.
In Britain, preparations to protect the civilian population had already been made in the years leading up to war. These were stepped up after the fall of France. Air raid shelters were constructed in streets and gardens. Gas masks were issued to everyone and arrangements were made for the evacuation of children from major cities. They were sent to the countryside or overseas to Canada, Australia and New Zealand. Defences were built all over southern England, beaches were mined and the Army, Navy and Air Force put on invasion alert.
In 1940 the Local Defence Volunteers were formed. They consisted of individuals too old or too young to be assigned to front-line units, or people in reserved occupations. The organisation was eventually re-titled the Home Guard and was a defence against possible German invasion. The units were improvised and poorly equipped, but they were dedicated to their duties and helped maintain morale during the dark days of 1940.
The Auxiliary Territorial Service (ATS) also protected the Home Front. Formed in 1938, the ATS recruited women to work as telephonists, drivers, mess orderlies, postal workers, ammunition inspectors, radar operators, gun crew and military police. By June 1945, there were over 190,000 members of the ATS from all across the British Empire.
The first German bombs fell on central London on 24 August 1940. This was probably a mistake by German bombers who were aiming for industrial targets around the Thames estuary.
Royal Air Force (RAF) retaliation on Berlin soon followed. The Germans then responded by bombing industrial targets and civilian centres across Britain in an attempt to 'soften up' the population and destroy its morale before Operation SEALION, the planned German invasion. This was a strategic error as it shifted the focus of the German air campaign away from Fighter Command's hard-pressed airfields. The RAF's subsequent victory in the Battle of Britain (10 July-31 October 1940) made Hitler cancel the invasion.
Although many other British cities were bombed, it was the constant bombing of London between September 1940 and May 1941 that was termed the 'Blitz'. More than 20,000 Londoners were killed and 1.4 million were bombed out of their homes during this period. One in every six people in the capital had no place to live. Around 5,000 members of the Pioneer Corps, armed with picks and shovels, helped clear the rubble and debris.