1. A junior officer and NCO from an unidentified Feldartillerie regiment wearing a portable sound locating apparatus, c. 1917
2. A two-horn system at Bolling Field, USA, near the Army War College at Fort McNair (in the background), 1921
3. An early Goerz listening equipment with receiving shells
4. Horn-like sound locators of the US Army
5. The Doppelt Richtungshörer, produced by the German Askania
6. A Barbier, Bénard et Turenne device from France
7.A Dutch device, built from 1934 for the Engineers Regiment and the Netherlands Army in the East Indies
8. Miniaturized listening devices for the improved mobility, concepts from The Netherlands, 1930s
9. Gigantic trumpet-like Japanese electric ears for detecting enemy planes, 1936
10. "Big Ears" Listen for Airplanes, 1938
11. A Japanese detector from the late 1930s
12. A four-horn acoustic locator in England: 1930s
13. The German Ringtrichterrichtungshoerer (or RRH) acoustic locator, mainly used in World War II antiaircraft searchlight batteries for initial aiming of the searchlights at night targets.
14. The Shout-O-Phone from 1940
15. Soviet soldiers are listening to the sky with their ZT-4 locator, 1942
