Japanese War Tuba.

This tuba-like device was actually the Japanese military’s acoustic locator – a device with which one can "hear" distant engine noise of oncoming airplanes.

Acoustic locators like this (and others) were used from mid-World War I through the early days of World War II, until the invention of radar made them obsolete.

Japanese War Tuba [wiki] | More neat pics at: Acoustic Radar