Perhaps having to wait for high tide at its destination?
Timing for a favorable tide is a valid theory to bring up. However, weird maneuvers indicated by the merchant ship’s position plot is a strange way to do this timing. It is less expensive and easier just to reduce speed and keep to the best safe course.
Was anyone even in command of the merchant ship’s bridge?
None the less, any collision is ultimately the fault of both ships. No matter of the “rules of the road for the stand on versus give way vessel, every captain is completely responsible for avoiding a collision.
Was this collision intentional? Was there a reason that the USN ship was unable to maneuver to avoid collision?