The Vikings primarily relied on oars for propulsion during naval operations. Their longships were designed for speed and maneuverability, and the use of oars allowed the Vikings to navigate effectively in various conditions, including shallow waters and strong currents. Sails were sometimes used as a supplementary means of propulsion, particularly during long-distance journeys or in favorable wind conditions. However, the Vikings primarily relied on their oars for controlling the direction and speed of their vessels in combat and while exploring vast bodies of water.