This week that ship has its last big outing. Moored in Hong Kong harbour, she will be used to bear away the last remnants of the British Empire from the colony - or the Special Administrative Region, as it will be by then. Everything in the world around her has changed during four decades; everything but the rain, that is. As she steamed in on Monday, dwarfed by the vast glass and steel towers that line the hills around the harbour, she was swept by a light tropical drizzle.
It is the last time that she will bring a dash of Fifties glamour to a state event. She is, in the judgement of the Government, too expensive to refit, and she will be decommissioned later this year. For her last appearance on the world stage, she has been given a character role in the handover of Hong Kong, hosting the dinners and drink parties, and then whisking away the Prince of Wales and the former governor Chris Patten. It is a role for which she was custom-built: the last imperial transport. In her 44 years, she has sailed more than a million miles, ferrying the Queen and the Royal Family around the Commonwealth.
When the young Queen christened her yacht in April 1953, there was still a Chief of the Imperial General Staff; indeed, there was still an Empire, or at least its remnants. The main foundation had gone in 1947, when India was partitioned and made independent; but the rest remained, a vast assembly of territories and colonies spread across the world. The Royal Family was at perhaps the peak of its popularity, with much talk of the new Elizabethan era; Britain was emerging, blinking but optimistic, into the post-war, Cold War world.
Britannia was supposed to represent continuity. She replaced the Victoria and Albert, the ageing 50-year-old boat which the Queen's father, George VI, had used. But she was to be very different, larger and more modern than the V&A, more streamlined, with a modern clipper bow and modified cruiser stern rather than the traditional swan bow and counter stern of previous royal yachts.
The Royal Yacht has a complement of 21 officers and 229 men, all specially selected from volunteers. She also carries, for special occasions, a Royal Marines band, an accoutrement that few large yachts can boast, made up of a director of music and 26 musicians. She was designed with two functions in mind: as a home-from-home for the monarch, but also as a hospital ship in time of war. The latter is a function that she has never carried out; indeed, when it was considered sending her to the Falklands in 1982, it was pointed out that she used the wrong fuel and would be hard to replenish in the South Atlantic.
She has, once, seen action, when she rescued British and other foreign residents caught in the crossfire during the 1986 civil war in South Yemen. Britannia was anchored off Aden, once one of Britain's most important overseas naval bases and the last bastion of the "East of Suez" policy; Britain was chased out, virtually at gun point, in 1967. She returned to Aden earlier this year, but this time on lighter duties. Britannia's last outing has taken her through several Asian and Arabian ports, in the cause of trade promotion.
Yet claims about Britannia's much discussed "business function" seem madly overdone. Only about 63 days were devoted to trade promotion in the seven years 1989-96, according to the last government. Indeed, the Queen herself used the vessel for only 11 days in 1996. Her role is primarily symbolic, as most supporters and opponents of the Royal Yacht would concede; yet that symbolism is hard to unpick. Supporters see it as a useful emblem of a maritime nation that treasures its history and traditions. Opponents see it as a waste of money, a symbol of a decaying state fixated with the past.
The truth is that Britannia is to some extent both: she is a product of one attempt to redefine the monarchy for a new age. She represents tradition, with her fine polished brass and teak decks, but also an effort to popularise the monarchy and open it up through travel. The kings and queens before Elizabeth II rarely set foot outside Britain, and made few visits to the Empire. For the Queen, travel has been vital: it has been used to cement the link between Britain, the monarchy and the Commonwealth.
Virtually all of the territories ruled from London in 1953 have become Commonwealth members, and the vast majority have a coastline. Britannia has been to almost all of them.
Yet the age in which she was conceived is - though only 40 years past - rapidly becoming almost unimaginably remote. There was little criticism of the Royal Family in 1953. Britain had, after all, just gone through the Second World War, in which the young Princess Elizabeth had regularly been seen in her ATS uniform, doing her bit for the country; a world away from the young Princess Diana selling her gowns at auction in New York. Opposite Westminster Abbey was a large open space left by the Luftwaffe's bombs which was earmarked as the new headquarters for the Colonial Office. It was to be neo-Georgian, eight storeys high, with twin flagstaffs on the roof. The winds of change were not even a twinge of indigestion in 1953.
It is no surprise, then, that the image Britannia projects is a little antique. The lifestyle that she represents is a kind of austere and public luxury, something which modern members of the Royal Family seem to have found a little harder to adjust to than the Queen. Jonathan Dimbleby, in his authorised biography of Prince Charles, describes the honeymoon voyage: "Even an intimate dinner by candlelight was hardly a private affair, accompanied as it was by the camaraderie of senior officers at the table and a band of Royal Marines playing a romantic medley in the background."
The Hong Kong trip will not be the Royal Yacht's last. Later this summer, she will, once more, tour the Western Isles, before finishing her long journey in Aberdeen. After that, it is anyone's guess where she will go, or what (if anything) will replace her. Among the buyers cited in the press over the past year have been Michael Jackson and Richard Branson; doubtless others will surface. Perhaps she will become a tourist attraction, like the poor sad Queen Mary at Long Beach.
After the row this year over her replacement, it remains to be seen whether private capital is drafted in to build a new yacht, and what it might look like. Last week three designs were trotted out at a seminar in Newcastle - a training yacht, a gin palace and a cruise liner, as one of those present described them. There is no guarantee that any of these will ever see the light of day; it may be that Britannia is the last of the line.
Britannia took her name from a shore-based establishment, the Royal Naval College in Dartmouth, which in turn had it from a wooden training ship anchored in the River Dart until 1914. But there have been other Britannias. Edward VII had a racing yacht called Britannia, launched on the Clyde in 1893 and the pride and joy of his son, George V. A previous Britannia was the flagship of the Mediterranean fleet, taking part in innumerable operations from the Crimea to North Africa. This was the real foundation of British power in the 19th century: a naval force that dominated the world's waterways. It was the Royal Navy that forced open China, routing the Chinese and forcing them into the humiliating Treaty of Nanking which ceded Hong Kong Island to Britain in perpetuity. This was a strategic force with a power, scope and range that the world had never experienced before.
The Royal Yacht Britannia is a pale shadow of that, the last echo of a trumpet blast. It is a signifier without a signified, an emblem of a powerful naval state without anything behind it. The Fifties saw the emergence of competitors to British shipbuilders, a trend that would wipe out most of the British yards over the next 30 years. The shipyard that built Britannia, John Brown and Co, went through hard times and has become Kvaerner Energy which no longer makes ships.
The Royal Navy is a shadow of its former self. The Merchant Navy is all but gone. The naval bases that sustained maritime supremacy have disappeared one by one, with Hong Kong the last (unless one counts the windswept inlet of Mare Harbour in the Falklands). Britannia no longer rules the waves. She may be replaced as a ship, but as a piece of symbolism, she has outlived her era.
Britannia as she was at launch in April 1953. 1) Royal drawing- room 2) Royal ante-room 3) veranda 4) guest cabins 5) the Queen's bedroom 6) the Duke's bedroom
7) the Queen's wardrobe room 8) entrance 9) the Queen's sitting-room 10) Royal dining-room 11) Royal barge (garage behind) 12) Royal sculleries (kitchen behind)
13) wardroom galley (pantry on right) 14) wardroom
15) Royal charthouse 16) crew space 17) engineers' workshop 18) stabiliser fin 19) auxiliary machinery room 20) crew's wash places 21) doctor and sick bay 22) oil fuel tank 23) boiler room 24) engine room 25) offices 26) staff cabins 27) guest cabins (right), air conditioning (left) 28) steering gear 29) baggage space 30) stores