BERLIN — Chancellor Friedrich Merz promised a year ago that Germany would have “the strongest army in Europe,” but turning words into tanks, missiles and planes is proving to be very difficult. The buildup is a direct result of Russia's full-scale invasion of Ukraine over four years ago — prompting Berlin to unleash billions to turn the Bundeswehr back into a military capable of fighting a war. In one crucial step aimed at speeding rearmament, Defense Minister Boris Pistorius on Wednesday moved