This was the first body-blow to the seemingly invincible German war machine

That the defeat of Germany and victory in Europe was possible at all in 1945 was not something that hinged solely upon the success of D-Day and the subsequent relentless advances on Germany from the west - as the Soviet Union closed in from the east. Instead, it was a victory that owed everything to the first body blow of the war - dealt to what had hitherto seemed to be an invincible German military machine. That body blow was the Battle of Britain.

It was something that "held the line" and made possible all that would follow on an arduous road to the defeat of Nazi Germany. However, Britain's earlier defeat in Europe during 1940 had seen the withdrawal from Dunkirk of the British Expeditionary Force; an event acknowledged by Prime Minister Winston Churchill as a military disaster, as well as a great deliverance. However, he was at pains to point out that wars were not won through defeats.

With Churchillian aplomb, his speech of June 18, 1940, set the scene for what lay ahead as he coined the phrase "Battle of Britain" for the very first time. "What General Weygand called the Battle of France is over," he said. "I expect that the Battle of Britain is about to begin. Upon this battle depends the survival of Christian civilisation. Upon it depends our own British life, and the long continuity of our institutions and our Empire.

"Let us therefore brace ourselves to our duties, and so bear ourselves that, if the British Empire and its Commonwealth last for a thousand years, men will still say, 'This was their finest hour.'" It was stirring stuff and Britain, her Empire and her allies needed it to stiffen resolve in the face of the very darkest of days. That Churchill should have made his speech on June 18 was prescient, for the following day the Luftwaffe launched its first major bombing raid against the British Isles.

Nevertheless, the battle was retrospectively declared to have begun on July 10 and to have run until October 31. In fact, these dates were entirely artificial and had little to do with the reality of actual events. They were set afterwards by Air Chief Marshal Sir Hugh Dowding, Commander-in-Chief of RAF Fighter Command during 1940.

It was an attempt to define the battle and its scope but by Dowding's own admission the dates were "somewhat arbitrary" and simply reflected the period when the heaviest fighting took place.

Essentially, the Battle of Britain might be portrayed as a "David versus Goliath" struggle as the pilots of RAF Fighter Command wrestled against daunting odds to deny the Luftwaffe air superiority. An ascendency over the RAF was necessary for Germany before it could consider attempting any seaborne invasion of the British Isles.

When battle finally began in earnest - whatever dates one might wish to apply to its timeframe - it caught the national imagination more so than any other of Britain's wartime clashes. This was simply because it was fought out in the skies over the country, principally over the South-East and London - in full view of the British public and press.

Whilst the civilian population had been exposed to terrifying attacks by Zeppelin airships and aircraft during the First World War, the Battle of Britain was the first time the public were on the frontline; they could literally watch the greatest aerial assault the world had yet seen. From their grandstand view of encounters unfolding above their heads, the public's admiration for the RAF's young fighter pilots grew. In fact, it would be true to say this admiration became adulation and hero worship as the battle progressed.

Perhaps this was increasingly the case as a realisation dawned they were seemingly all that stood between potential defeat and the catastrophe of invasion. August 13, 1940, today known as Eagle Day or "Adlertag", was the first day of Unternehmen Adlerangriff ("Operation Eagle Attack"), an air operation by the Luftwaffe intended to destroy the RAF. The Daily Express front page of August 14 declared: "Biggest air raids of all" with a sub-deck stating, optimistically: "RAF shoots down 39 more Nazis and loses only nine fighters."

Published losses of German aircraft and the RAF defenders was almost always incorrect. In respect of the Luftwaffe's losses, claims were mostly over-optimistic due to a number of factors, not least the confusion of battle. Pilots often ended up claiming an aircraft as destroyed that had also been claimed by others. Untangling the confusion was not possible until long after the event - and, in any case, over-inflated figures suited British propaganda and boosted morale.

On August 12, for example, only eight enemy aircraft fell on land, although around 20 or so fell at sea or crashed in France. Mostly, the RAF would be unaware of those losses anyway. On the other hand, RAF losses were often underrepresented. On August 12, around 24 fighters were lost - significantly more than the nine mentioned in news reports.

Churchill spoke for the nation when he declared to the Commons on August 20: "Never in the field of human conflict was so much owed by so many to so few." Henceforth, of course, these pilots would be immortalised as "the Few".

Such was the significance of the struggle that it the only battle of either world war to have had a special commemorative date established: Battle of Britain Day. It also marked a critical turning point. On September 15, 1940 - a Sunday - the Luftwaffe launched one of its biggest attacks on London in the hope of drawing the RAF into a fight of annihilation. Around 1,500 aircraft took part in the air battles, which lasted until dusk.

Never were the Luftwaffe to send so many planes - and, starting on September 7, the Blitz increasingly occupied the minds of Hitler and Germany's generals.

As bombs began to fall on Britain in an ever-increasing tonnage, so the RAF's fighter pilots were pretty much the only effective defence. Thus, they were rightly perceived as saviours of the nation. But it would be wrong to view victory during the Battle of Britain as a decisive one for the RAF. It wasn't. Instead, it might not be unreasonable to view the outcome as a home draw.

Nevertheless, the outcome was the same as if an all-out decisive defeat of the Luftwaffe had been achieved and it was an outcome that prevented Germany from going on to the next round, as it were.

Eighty-five years on, the Battle of Britain still holds a remarkable place in the collective memory of the peoples of Great Britain, her Commonwealth and the free world. It was a struggle which united airmen from no less than 15 nations - including the occupied countries of Europe - against the Nazi menace.

But it was also a battle on which national survival depended if Germany was to be prevented from launching Operation Sealion, the invasion and occupation of the British Isles. Longer term, it ensured the continuation of the war against Germany.

Having held the line, the brave pilots of RAF Fighter Command effectively set the agenda for the immediate conduct of the war from the end of 1940 onwards. That agenda would lead to Hitler abandoning his aims of invading and neutralising Britain and then to his disastrous invasion of the Soviet Union during the following spring.

As events began to unfold on the back of the Battle of Britain, the next two years saw the United States enter the war, the German armies being stopped at Stalingrad and the British opening an offensive at El Alamein that would see Rommel's forces in full retreat across Africa.

It was also a period that saw its share of defeats, including in the Far East. However, when Churchill came to write his fourth volume of the history of the Second World War, he called it The Hinge of Fate. Of victory at El Alamein, he said: "This is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning." That this hinge could turn at all had been made possible by a "holding of the line" by the RAF's fighter pilots in 1940. Its longer-term significance, and on ultimate victory secured five years later, cannot be underestimated.

That "home draw" during the Battle of Britain had arguably been the most important outcome of any of the battles during the Second World War.