Best known as the world's first cruise line, P&O is a great choice for anglophiles looking to immerse themselves in Britishness. The fleet of seven mid-size and large ships attract a clientele that’s fiercely loyal, reveling in the traditional interpretation of cruising. (Picture early and late seatings at dinner with assigned tables, and a band that heralds your departure as the ship sails away.) It makes sense that the line — now part of Carnival Corporation — sticks close to the early traditions of cruising: It is generally accepted that P&O actually invented cruising following its founding in 1837. The company, then known as the Peninsular and Oriental Steam Navigation Company, placed an ad in a Scottish newspaper for a roundtrip voyage using the company’s burgeoning fleet of merchant ships. The rest, as they say, is history.