Credit World War I for putting the pressure on Rolls-Royce to expand from cars to planes. Already one of the young auto industry’s premier manufacturers, the British company was reluctant to follow the urging of its government to start making aircraft engines for the war effort. But when they did—in 1914 under a license with Renault, a year later under their own brand—the firm brought the same level of craftsmanship and reliability to that effort that Rolls-Royce had come to represent. Good thing, too. Today, Rolls-Royce is the second-biggest aircraft engine manufacturer in the world, behind GE. Split into separate companies decades ago, the aircraft engine business dwarfs the luxury car racket.