Russia planned to assassinate the CEO of a major German arms manufacturer that provides artillery ammunition and armored vehicles to Ukraine, but the plot was uncovered and disrupted by U.S. and German authorities, according to a U.S. official and a source with knowledge of the matter. The alleged plot targeted Armin Papperger, the chief executive of Rheinmetall AG, Europe’s largest producer of ammunition, whose company makes 155 mm artillery rounds for Ukraine and plans to open several plants...