The stern hull portion of a surface ship or underwater sea craft is provided with a waterjet propulsion unit having an outlet end from which a discharge propelling waterjet emerges underwater and undergoes flow beyond the stern end of the hull between a pair of twin contoured rudders normally positioned for straight forward propulsion of the hull. The contoured rudders pivotally mounted underwater on the hull are angularly displaced by maneuvering control in opposite directions from the normal positions to maneuvering positions with their lower end tips in contact with each other to form a bucket to directionally change flow of the emerging waterjet for steering, deceleration and backing purposes during hull propulsion between low and high speeds. The twin rudders are also angularly displaced by the maneuvering control in the same angular direction for a different directionally regulated change in waterjet flow to effect turning of the hull for propulsion in a reverse direction.