The massive disposal effort, which U.S. military officials call unprecedented, has unfolded largely out of sight amid an ongoing debate inside the Pentagon about what to do with the heaps of equipment that won’t be returning home. Military planners have determined that more than $7 billion worth of equipment — about 20 percent of what the U.S. military has in Afghanistan — will not be shipped back, because it is no longer needed or would be too costly to send home. That has left the Pentagon in a quandary about what to do with the items. Bequeathing a large share...