Recognised as the first British company to operate regular sea cruises, P&O has a history that goes back to 1837. In more recent times, P&O has undertaken a shift away from line voyages to operating cruises full time. The purchase of Princess Cruises in 1973 led to the founding of the company we know today. Here, Roger Cartwright tells the story of P&O Princess's illustrious history as a cruise line, from the Vectis, the world's first dedicated cruise ship to the Grand class ships of today, each carrying almost 3,000 passengers and weighing in at over 115,000 tons each.