Japanese War Tubas

In this picture taken in the 1930s, you can see Japanese Emperor Hirohito inspecting a fleet of giant tubas, with anti-aircraft guns in the background. They were actually using these acoustic locators that looked like tubas to "listen" to the enemy aircraft engines.

Acoustic location was used from mid-World War I to the early years of World War II for the passive detection of aircraft by picking up the noise of the engines. It was rendered obsolete before and during World War II by the introduction of radar, which was far more effective.

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