WHEN THE MARINES decided to buy a helicopter-airplane hybrid "tiltrotor" called the V-22 Osprey, they saw it as their dream machine. The tiltrotor was the aviation equivalent of finding the Northwest Passage: an aircraft able to take off, land, and hover with the agility of a helicopter yet fly as fast and as far as an airplane. Many predicted it would reshape civilian aviation. The Marines saw it as key to their very survival. By 2000, the Osprey...