The Defense Department is laying the groundwork to begin a sweeping new mobility requirements study in 2019, an assessment that will revise the requirement for the total number of aerial refueling tankers, cargo aircraft and supply ships the U.S. military requires to support the defense strategy commissioned by the Trump administration and expected to be complete later this year. Air Force Gen. Carlton Everhart, head of Air Mobility Command, said U.S. military logisticians and policy makers expect to develop assumptions...