Dunkirk actor Harry Styles shows off his new 1940s-style military cut as he joins the Hollywood scale operation on WWII drama

The evacuation from Dunkirk was one of the biggest operations of the Second World War and was one of the major factors in enabling the Allies to continue fighting.

It was the largest military evacuation in history, taking place between May 27 and June 4, 1940.  The evacuation, known as Operation Dynamo, saw an estimated 338,000 Allied troops rescued from northern France. But 11,000 Britons were killed during Operation Dynamo, and another 40,000 were captured and imprisoned.

Described as a 'miracle of deliverance' by wartime prime minister Winston Churchill, it is seen as one of several events in 1940 that determined the eventual outcome of the war.  

The Second World War began after Germany invaded Poland in 1939, but for a number of months there was little further action on land. But in early 1940, Germany invaded Denmark and Norway and then launched an offensive against Belgium and France in western Europe.

The evacuation from Dunkirk was one of the biggest operations of the Second World War and was one of the major factors in enabling the Allies to continue fighting

Hitler's troops advanced rapidly, taking Paris - which they never achieved in the First World War - and moved towards the Channel.

They reached the coast towards the end of May 1940, pinning back the Allied forces, including several hundred thousand troops of the British Expeditionary Force. Military leaders quickly realised there was no way they would be able to stay on mainland Europe.

Operational command fell to Bertram Ramsay, a retired vice-admiral who was recalled to service in 1939. From a room deep in the cliffs at Dover, Ramsay and his staff pieced together Operation Dynamo, a daring rescue mission by the Royal Navy to get troops off the beaches around Dunkirk and back to Britain. 

On May 14 1940 the call went out. The BBC made the announcement: 'The Admiralty have made an order requesting all owners of self-propelled pleasure craft between 30ft and 100ft in length to send all particulars to the Admiralty within 14 days from today if they have not already been offered or requisitioned.'

It was the largest military evacuation in history, taking place between May 27 and June 4, 1940. The evacuation, known as Operation Dynamo, saw an estimated 338,000 Allied troops rescued from northern France

Boats of all sorts were requisitioned - from those for hire on the Thames to pleasure yachts - and manned by naval personnel, though in some cases boats were taken over to Dunkirk by the owners themselves. 

They sailed from Dover, the closest point, to allow them the shortest crossing. On May 29, Operation Dynamo was put into action. 

When they got to Dunkirk they faced chaos. Soldiers were hiding in sand dunes from aerial attack, much of the town of Dunkirk had been reduced to ruins by the bombardment and the German forces were closing in.

Above them, RAF Spitfire and Hurricane fighters were headed inland to attack the German fighter planes to head them off and protect the men on the beaches.

As the little ships arrived they were directed to different sectors. Many did not have radios, so the only methods of communication were by shouting to those on the beaches or by semaphore. 

Boats of all sorts were requisitioned - from those for hire on the Thames to pleasure yachts - and manned by naval personnel, though in some cases boats were taken over to Dunkirk by the owners themselves

Space was so tight, with decks crammed full, that soldiers could only carry their rifles. A huge amount of equipment, including aircraft, tanks and heavy guns, had to be left behind.

The little ships were meant to bring soldiers to the larger ships, but some ended up ferrying people all the way back to England. The evacuation lasted for several days.

Prime Minister Churchill and his advisers had expected that it would be possible to rescue only 20,000 to 30,00 men, but by June 4 more than 300,000 had been saved.

The exact number was impossible to gauge - though 338,000 is an accepted estimate - but it is thought that over the week up to 400,000 British, French and Belgian troops were rescued - men who would return to fight in Europe and eventually help win the war.

But there were also heavy losses, with around 90,000 dead, wounded or taken prisoner. A number of ships were also lost, through enemy action, running aground and breaking down. Despite this, Dunkirk was regarded as a success and a great boost for morale.

In a famous speech to the House of Commons, Churchill praised the 'miracle of Dunkirk' and resolved that Britain would fight on: 'We shall fight on the beaches, we shall fight on the landing grounds, we shall fight in the fields and in the streets, we shall fight in the hills. We shall never surrender!'