The gathering feels like the opening of an upmarket car showroom. There’s free food and drink and guests stand around admiring the vehicles – even if they are not your everyday runabouts. These tanks and mobile missile launchers are carefully spot-lit and each carries a QR code for more information – but there are no price tags. “If you buy two,” says one suited man discreetly to another, both dwarfed by a green Lynx tank, “we can maybe talk ...” But these expensive attractions are just the warm-up act for what is unveiled with dry ice and a laser show:...