Ridiculous that this drill is just about N Korea. We do at least a summer drill every year with S Korea and other allies in S Korea from the northern region to down below Seoul and out towards the coastal areas as well as at sea.
S Korea and the USA have caught a share of N Korean spies creeping into Seoul and other areas occasionally. S Korea usually just shoot them coming in in scuba gear or sometimes already on land.
But. sometimes N Korean defectors or escapees from their country make their way into S Korea then given refuge in Australia, USA, or other countries.