I'm surprised there's so much confusion over this. Aircraft carriers have aircraft and before a ship full of pilots can fly their aircraft, they need to be certified to do so. In order to do that, they need to do training exercises for take offs during the day and during the night. You want to do these certifications in friendly waters. It doesn't mean the Carl Vinson strike group wasn't destined for North Korea. They were following standard protocol. Keep in mind also that these crews usually have hundreds of first time sailors onboard for their first six month tours. They need training too.