French soldiers wearing gas masks in a trench, 1917. Gas mask technology varied widely during the war, eventually developing into an effective defense, limiting the value of gas attacks in later years
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…