Which device is primarily used by a radio operator to locate other vessels?

A radar is primarily used by a radio operator to locate other vessels because it functions by emitting radio waves that bounce off objects, such as ships, allowing the operator to determine their distance and direction. This technology is crucial for navigation and collision avoidance in marine environments, especially when visibility is limited due to fog, rain, or darkness.

While sonar is primarily used for detecting underwater objects and navigating submerged environments, it does not serve the same purpose for locating surface vessels. GPS (Global Positioning System) is essential for determining a vessel's position and navigation but does not specifically help locate other vessels in the same active manner as radar does. A transponder, on the other hand, is used for identification and communication purposes, often in the context of Automatic Identification System (AIS) technologies, helping vessels understand their own position relative to others but not actively locating them in real-time like radar.