Working to meet a tight withdrawal deadline in Afghanistan, the U.S. military is destroying massive amounts of its own equipment that is too expensive to bring home. The unprecedented scrapping effort has destroyed about 170 million pounds of gear, worth about $7 billion. The military arrived at the decision because of complex laws governing donations of arms to other nations, and U.S. allies eligible to be given the equipment won’t want to pay to retrieve it. So the only choice was to trash 20 percent of the gear, crushing it and selling it for pennies per pound. “This is the largest retrograde mission in history,” Major General Kurt Stein said.