The U.S. Army has big plans to modernize its fleet, but faces some heavy fighting ahead.In March 2002, 1,700 U.S. troops brought the full power of American military technology to bear on 100 square kilometers of rough mountainside in Afghanistan. Unmanned aerial drones, sensor-laden ground robots, and satellites scoured the Shar-I-Kot valley for an estimated 1,000 al Qaeda and Taliban fighters hiding in crags and caves. But the electronic eyes did not see all. While the United States claimed victory in the battle 18 days after it started, nine U.S. soldiers were killed and scores—possibly hundreds—of enemy fighters escaped. The...