By Stephen Dalziel BBC Russian Affairs Analyst

The Russian President, Vladimir Putin, is taking part in the celebrations to mark D-Day, the opening of the "Second Front" in the war against Nazi Germany.

Sombre monuments to the Soviet sacrifice remain across Europe

It is the first time that a Russian leader has been invited to the ceremony.

The Russian - and before that, the Soviet - attitude to Operation Overlord has always been that the Western allies have never given proper recognition to the part played by the USSR in the defeat of Hitler's armies.

An estimated 27 million citizens of the Soviet Union perished in World War II.

By comparison, total casualties for the USA and Great Britain, military and civilian, are estimated at around 700,000.

From the moment that the USSR was brought into the War, by the German invasion of June 1941, Moscow was calling upon its Western allies to open a second front against Germany.

The Western view has always been that, so huge and complicated was the operation to cross the English Channel in secret, June 1944 was the earliest opportunity.

'Two years late'

Like many of his countrymen, Russian historian, Valentin Falin, author of the book The Second Front, disagrees.

Together we tried to conquer evil, and together create a better world - unfortunately, we didn't succeed with the second aim Valentin Falin Russian historian

He maintains that the Second Front was opened late, and that, as a result, the War dragged on, and tens of millions of lives were lost unnecessarily.

Dr Falin sets great store by the fact that the US General, Dwight D Eisenhower, suggested that the Second Front be opened in the summer or autumn of 1942.

President Franklin D Roosevelt initially agreed.

But the British Prime Minister, Winston Churchill, refused.

Dr Falin is in no doubt that this was because of Mr Churchill's dislike of the Soviet Union.

And he insists that, had the Second Front been opened then, "the Second World War in Europe would have ended no later than 1943".

The bitterness caused by what the Russians perceive as the late opening of the Second Front has continued many years after the end of the war.

And it was not helped 10 years ago, when the Western allies did not invite Russia to participate in the 50th anniversary of D-Day.

'Ignored'

Dr Falin believes not only that this was insulting, and a mistake, but that the allies made another important error.

In their speeches on that occasion, the Americans failed even to mention the Soviet Union.

"It was as if Germany had fought only in the West," says the Russian historian.

He then quotes British statistics, which show that 93% of the losses of the German Armed Forces were on the Eastern Front.

All of their others - in Western Europe, North Africa, the Atlantic Ocean - account for a mere 7%.

Bitter-sweet victory

But despite all this, Dr Falin is not bitter.

The most important thing, he muses, is that the outcome of the war was a victory for East and West.

And he concludes that, "together we tried to conquer evil, and together create a better world - unfortunately, we didn't succeed with the second aim."