Sonar in the modern, military-technology sense was developed during World War I, especially between 1915 and 1918, but the earliest sonar‑like listening device was invented in 1906 by American naval architect Lewis Nixon to detect icebergs.

Quick Scoop: When Was Sonar Invented?

  • 1490s: Leonardo da Vinci uses a simple tube-in-water trick to listen for distant ships, an early conceptual use of underwater sound for detection.
  • 1906: Lewis Nixon invents one of the first practical sonar‑type underwater listening devices to detect icebergs for ship safety.
  • 1912–1914: Interest in such technology grows, especially after the Titanic disaster and with more systematic experiments like Reginald Fessenden’s echo-ranging work, which detected icebergs at about 2 miles.
  • 1915–1918: True “sonar” (active echo‑ranging for submarines) is developed during World War I; Paul Langévin’s quartz‑based system in 1915 is often cited as the first modern sonar‑type device for submarine detection.
  • 1918: Operational passive sonar systems (listening for submarine noise) are in service by the end of World War I.

So if you mean:

  • “First sonar‑like listening gadget for hazards at sea?” → 1906 (Lewis Nixon).
  • “First modern wartime sonar to find submarines?” → Developed 1915–1918 in World War I, with key work by Paul Langévin and others.

In everyday terms, most historians place the invention of sonar as a technology in the World War I period (1915–1918), built on earlier ideas and devices from 1906 and even conceptual experiments centuries before.

TL;DR:
Sonar’s roots go back to Leonardo, its first practical iceberg‑detector appeared in 1906, and the fully recognizable military sonar systems were invented and tested during World War I (1915–1918).

Information gathered from public forums or data available on the internet and portrayed here.