DOVER AIR FORCE BASE, Del. — Virtually every day, a line of 18-wheel trucks loaded with weapons or ammunition pulls up to a sprawling warehouse here nestled near an asphalt runway stretching nearly two miles. Drawn from U.S. military depots around the country, the lethal cargo is unloaded onto pallets that will be packed aboard cargo planes bound for Europe, the next stop on its journey to the front lines in Ukraine.