Before the invention of radar in the 1930s, the British military constructed massive concrete structures known as acoustic mirrors along the southern and eastern coasts of England. These parabolic reflectors were designed to detect the sound of incoming enemy aircraft by focusing sound waves onto a central microphone. While they could successfully detect aircraft up to fifteen miles away under ideal conditions, their effectiveness was severely limited by atmospheric disturbances and the rapidly increasing speed of newer planes. As a result, when radar technology emerged, offering far greater range and accuracy, the acoustic mirrors were quickly rendered obsolete.
Which choice best states the main idea of the text?
- AAcoustic mirrors would have remained the primary method of coastal defense if aircraft speeds had not increased so rapidly.
- Acoustic mirrors served as an early aircraft detection system in Britain, but they were ultimately abandoned due to performance limitations and the advent of radar.Answer
- CAcoustic mirrors were highly reliable because they could focus sound waves onto a microphone from over fifteen miles away, regardless of weather conditions.
- DMilitary defense systems must constantly adapt to technological innovations to remain effective against foreign threats.
Answer
Acoustic mirrors served as an early aircraft detection system in Britain, but they were ultimately abandoned due to performance limitations and the advent of radar.
The passage introduces acoustic mirrors as early military structures designed for aircraft detection, outlines their operational limitations (atmospheric disturbances and aircraft speed), and explains how the arrival of radar made them obsolete. The correct option accurately summarizes this progression by identifying the system's role, its shortcomings, and its eventual replacement.
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