By Nicholas Witchell
Royal correspondent, BBC News
The Queen and Prince Philip are on a four-day visit to the country
It's a well-established fact that Queen Elizabeth doesn't do politics or diplomacy. Except, of course, that she does, most especially when she is on a state visit to a foreign country.
All such visits are chosen and controlled by the British Foreign Office. Their unashamed purpose is to further what British diplomats perceive to be Britain's interests abroad.
And there are few more potent message-bearers in the British diplomatic arsenal than its veteran head of state, widely recognised - by virtue of her 56 years on the throne - as the Western world's senior statesperson.
In coming to Turkey, the Queen is - at the behest of the Foreign Office - sending a very clear message in support of Turkey's aspiration to join the European Union and, by implication, to be Westward-facing.
But the underlying message of this state visit is both more subtle and more important than that.
It is a diplomatic cliche that Turkey stands at the crossroads between Europe and Asia - a country of 72 million people whose strategic significance is hard to overstate but which is sometimes overlooked.
So far as the West is concerned, Turkey can be said to be the most successful example of a Muslim country which has embraced democracy.
Potentially, as one Western diplomat put it, the country is an example to the rest of the Muslim world of how democracy can work.
In military terms, Turkey occupies an important strategic position, as was demonstrated in both Gulf wars.
The Queen visited the mausoleum of Mustafa Kemal Ataturk in Ankara
It is also of considerable significance in terms of counter-terrorism and the international efforts to defeat the smugglers of drugs and people - quite apart from its role as a route for vital energy supplies.
In short, Turkey matters.
But things are happening within the country's society which are worrying the West.
Ever since the modern Turkey was created in 1923 by Mustafa Kemal Ataturk, the country has prided itself on its secularism. Politics and religion have been kept completely apart.
Today, though, the demarcation is becoming increasingly blurred. Last year Turkey elected a new president, Abdullah Gul, whose background is in political Islam.
The changes in the country manifested themselves in a small but highly symbolic moment on the first day of this visit.
When the president and his wife, Hayrunnisa, welcomed the Queen and Prince Philip to their official residence, Mrs Gul was wearing a headscarf - notwithstanding well-established protocols in Turkey that headscarves amount to a religious statement and therefore may not be worn in public buildings.
The gesture by the wife of the Turkish president will inflame the sensitivities between the country's Islamists and its secularists.
Already Turkey's army which, for generations, has regarded itself as the principal guardian of the country's secular constitution, has issued subtle warnings that it will not stand by and allow Turkey to become an Islamist state.
In the past the military has not hesitated to intervene to overthrow governments of which it had disapproved.
So there is a pressing need, in Britain's view, to bolster Turkey's ambitions to join the European Union and, thereby, to encourage European values and freedoms and to hasten fundamental changes in the areas of economic efficiency and political stability.
Among those, of course, are the important issues of human rights and freedom of speech.
To that end then, Queen Elizabeth has been pressed into service.
Her presence in Turkey and Britain's strong support for the country's EU candidature (in the face of strong opposition from France and others) will reassure the secularists and those Turks who are westward-facing, that they have influential allies.
It is also evidence that, at the age of 82, Britain's head of state can still cope with four days of engagements in Turkey's early-summer heat, and that she still packs quite a diplomatic punch.