War tubas!

An interesting bit of history.....

The Japanese war tuba

Photograph featuring two Japanese acoustic locators mounted on 4-wheel carriages, taken in the 1930s

The Japanese war tuba (Known in Japanese as: 九〇式大空中聴音機, "Large air sound detector ninety formula") is a colloquial name sometimes applied to Imperial Japanese Army acoustic locators due to the visual resemblance to the musical tuba. The name derived from a misidentification, possibly in jest, of a historical photo from the 1930s featuring the Japanese emperor Shōwa inspecting the acoustic locators with anti-aircraft guns in the background.

Acoustic location

Acoustic location devices were used by military services from mid-World War I to the early years of World War II for the passive detection of approaching enemy aircraft by listening for the noise of their engines. These typically consisted of large acoustic horns attached to stethoscope-type earphones worn by monitors. This technology was rendered obsolete before and during World War II by the introduction of radar, which was far more effective. Some examples of parabolic concrete acoustic location

Source: http://military.wikia.com/wiki/War_tuba