How Sonar Actually Works

IN THE EARLY DAYS OF WORLD WAR II, ALLIED navies faced a stark challenge: how to detect Germany's growing fleet of U-boats and prevent them from repeating the havoc wrought in World War I

- Kyle Mizokami

While German subs exacted a horrifying toll in the years between 1939 and 1945, a new technology-sonar-helped the Allies locate and sink Axis submarines. Today, sonar has evolved into a sophisticated military tool used in everything from submarines to helicopters, stalking both surface and subsurface targets with one goal: dominance of the world's oceans.

Active Sonar // This type of sonar involves a warship broadcasting directed sound waves underwater: If the sound waves strike an underwater object such as a sub, they're reflected back to the ship, which registers it as an object worth investigating. The ship can determine the distance of the object by counting how long it takes for sound waves to return. Repeated returns can even allow sub hunters to determine if an object is moving, what direction it's moving in, and how fast it's going.