WASHINGTON — Ever since the Army lost its warplanes to a newly independent Air Force after World War II, soldiers have depended on the sister service for help from the sky, from bombing and strafing to transport and surveillance. But the wars in Iraq and Afghanistan have frayed the relationship, with Army officers making increasingly vocal complaints that the Air Force is not pulling its weight. In Afghanistan, Army officers have complained about bombing missions gone awry that have killed innocent civilians. In Iraq, Army officers say the Air Force has often been out of touch, fulfilling only half of...