WAITING TO HEAR FROM YOU

   Before radar, mechanical acoustic devices made up the bulk of air defense strategies during WWI and early WWII. Loud fighter plane propellers were easily detected and provided up to several minutes of advanced warning at a distance of a few miles. Britain even used large concrete sound locators along its coastlines with a detection range up to 10 to 15 miles and up to a 15-minute warning of a Zeppelin approaching at a speed of 60 miles an hour. But by the late 1930's, fighter planes were able to reach speeds from 190 to 240 miles an hour which dramatically reduced early detection by these listening devices obsolete; effectively rendering them obsolete. By 1939, radar technology developed to become the primary air defense system with greater detection ranges of up to 80 miles. Depending on the country, the acoustic listening devices were colloquially known as "sound trumpets," "sound locators," "listeners," or "war tubas."