Rodney Wade Billman, age 9, of Williamsport, ] Pennsylvania, for his question:

When was radar first used?

Radio Detection And Ranging    string the capital letters together and you get the five letter word RADAR. Radio waves were discovered early in the 1800s and scientists started testing them. Late in the 1800s, they learned enough to send signals by invisible radio waves. More tests were made to learn what else radio could do.

In the 1930s, U.S. Navy scientists stumbled upon something new. Radio signals bounced off a boat and returned to the sender. This radio echo trick led to the invention of radar.

American and British scientists worked with experts in electronics to make it possible. The first radar systems were ready in time for World War II. In 1939, the British had radar stations set up to warn them when German bombers were on the way. Ships had radar to detect enemy submarines. These first radar systems of World War II were very useful indeed. But all sorts of improvements were made in the next 30 years. Modern radar systems work for pilots and airports, for the weathermen and the latest models even help astronomers to scan the starry skies.