Turkish troops use a heliograph at Huj, near Aza City, in 1917. A heliograph is a wireless solar telegraph that signals by flashes of sunlight usually using Morse code, reflected by a mirror.
American troops using a newly-developed acoustic locator, mounted on a wheeled platform. The large horns amplified distant sounds, monitored through headphones worn by a crew member, who could direct the platform to move and pinpoint distant enemy…
German submarines in a harbor, the caption, in German, says "Our U-Boats in a harbor." Front Row (left to right): U-22, U-20 (the sub that sank the Lusitania), U-19, and U-21. Back Row (left to right): U-14, U-10, and U-12.