When the Queen last visited South Africa in 1947 she went by battleship with her parents, King George VI and Queen Elizabeth.

That was still a respectable way for heads of state to travel.

At 44,500 tons, HMS Vanguard was the biggest warship to be built in Britain - larger (just) than the largest aircraft-carrier.

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Battleships were designed for command in war and minimal modifications were necessary to make Vanguard fit to carry a king, a queen and the heiress presumptive to the throne.

Today, the Royal Navy has no battleships and the present Vanguard is a Trident submarine.

Tomorrow, the Queen will fly to South Africa on a chartered Boeing 767.

In 1947, there were few commercial aircraft. The British Overseas Airways Corporation had just introduced the Constellation, but these sleek, propeller- driven aircraft could not make South Africa in a single bound.

If the royal party had travelled by air, there is a good chance it would have gone by flying-boat, stopping at harbours and lakes for several nights on the route.

Vanguard left Portsmouth on 1 February 1947 and arrived in Cape Town 16 days later.

It was the first time Queen Elizabeth - now the Queen Mother - had left Britain in nearly eight years and the first time the Princesses Elizabeth and Margaret had been abroad.

When the "royal firm" left Britain, the country was in the grip of the worst winter of the century.

George VI intended to thank South Africa for its part in the war. But he worried about conditions at home, saying he thought he should have stayed.

The press agitated for his return, feeling that the Commonwealth countries did not deserve so much attention.

When the ship passed the Canary Islands, spirits lifted. But it was on the voyage that astute royal-watchers first noticed there was something wrong with King George VI.

He had cramp in his leg and was losing weight. During the visit he was constantly worried by the heat and driven to outbursts of temper.

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When the royals visited South Africa in 1947, the party in power was led by Field Marshal Jan Smuts, who had been their guest at Windsor during the war.

On 17 February the whole family was up early, scanning the coastline of South Africa as Vanguard steamed towards Table Mountain. During their visit they travelled mostly by train, although they flew to the Northern Transvaal and to Southern Rhodesia, now Zimbabwe.

The party's mood plunged after an incident described recently by Group Capt Peter Townsend, Equerry on the tour to King George VI.

In Benoni, an African broke from the crowd and reached the running-board of the royal open car.

The Queen, fearing for the safety of the young princesses, hit him several times with a parasol before police dragged him away and knocked him senseless. Only later did it emerge that he had been trying to press a 10-shilling note into Princess Elizabeth's hand as a birthday gift.

Vanguard left Cape Town on 24 April 1947. After his return, the King referred to the magnitude of South Africa's task. "Adjusting from day- to-day the progress of a white population of well over 2 million with that of a far greater number of other peoples, very different in race and background ... There is no easy formula for the wise discharge of this formidable task."

The formula chosen, from May 1948, was apartheid.