A mock air battle between an F-16 jet and the military’s new and oft-troubled F-35 stealth jet showed that the F-35 is too sluggish to hit an enemy plane or dodge gunfire, according to a report. The F-35 has cost the US military more than a trillion dollars since work on it began, making it the most expensive weapon in history. The mock air battle, staged in January over the Pacific Ocean, was to...