The Army has deployed a new troop transport vehicle in Iraq with many defects, putting troops there at unexpected risk from rocket-propelled grenades and raising questions about the vehicle's development and $11 billion cost, according to a detailed critique in a classified Army study obtained by The Washington Post. The vehicle is known as the Stryker, and 311 of the lightly armored, wheeled vehicles have been ferrying U.S. soldiers around northern Iraq since October 2003.