By Peter Caddick-Adams
As Prince William graduates from Sandhurst, why do the world's ruling elite flock to military academies?
William being put through his paces
For many of the world's rulers, sending their offspring to a military academy is a sort of finishing school.
Often they choose Sandhurst, the military college in Surrey where officers have trained since 1812. Graduating alongside Prince William on Friday will be 19 overseas students.
Past graduates include the heads of state of a dozen countries - the Kings of Jordan and Malaysia, the Emir of Qatar, and the Sultans of Brunei and Oman. Winston Churchill attended the military academy, as did singer James Blunt, writer Ian Fleming, actor David Niven, photographer Patrick Lichfield, and legions of businessmen as well as Dodi Al Fayed.
So what is the magic formula that Sandhurst offers?
The UK has three officer academies - Dartmouth on the south Devon coast for the Royal Navy, Cranwell in Lincolnshire for the RAF and Sandhurst for the British Army.
Although William's father, Prince Charles, graduated from Dartmouth, where he was following his father's tradition of naval service, arguably Sandhurst is a different league.
Do one's chores
For one thing, training at a military college - particularly Sandhurst - is a great social leveller.
The students may be crown princes and princesses, or the children of lorry drivers, but background doesn't matter as future male and female officers embark on their strenuous 44-week course, divided into three terms.
The late King Hussein of Jordan (centre) trained at Sandhurst
Officer cadets find themselves polishing boots, ironing shirts, facing intensive drill sessions and enduring gruelling physical training. For future rulers, this may be the only time in their lives they have to do all their own laundry.
Sandhurst is a military base and thus a secure place for royals and future rulers to train and study - and they do both for nearly a year.
Unlike West Point in the United States or St Cyr in France, the royal military college is not a university as 85% of each class are already graduates.
Each September, January and May a new intake of 270 entrants, divided into three companies of about 90, begin the most exacting series of intellectual and physical tests they will probably experience in their lives. About 15% will fail to complete the course.
As well as extensive calls on their physical stamina - with no special treatment for sheikhs or princes - cadets also study international affairs, conflict and communication skills.
UK cadets like William and Harry, who graduated from Sandhurst last April, are bound for a three-year post as an army officer. Some stay on as career officers, but many leave and enter a diverse range of walks of life.
The bonds formed under pressure at Sandhurst can be lifelong. And the long-term benefits of this kind of networking for the royals and others destined to rise to future prominence can be imagined.
Prince Harry graduated in April
But access is not guaranteed. A Sandhurst place is secured only via the Army Officer Selection Board, long recognised as one of the most rigorous recruiting systems in the UK and much imitated by the private sector.
Officer Cadet William Wales becomes a second lieutenant at midnight. As he slow-marches up the steps of Old College in time to Auld Lang Syne, in a timeless military tattoo called the Sovereign's Parade, he can reflect that he has survived the most exacting education that money cannot buy.
For Sandhurst, and other military colleges, are all about how a person is as a leader, not who they are.