“WE ARE WORKING flat-out,” says Armin Papperger, chief executive of Rheinmetall, Germany’s biggest arms-maker. Ever since Russia invaded Ukraine in February last year, the Düsseldorf-based maker of tanks, ammunition and other military kit has been inundated with orders. On August 10th the firm reported that sales of its military ware in the first half of the year had risen by 12%…