What was used in WW1 to detect submarines?

During World War I, several methods were employed to detect submarines, including hydrophones (underwater microphones) and sonar technology, which were still in their early stages of development. Ships also used depth charges and patrolling aircraft to locate and attack submarines. Additionally, the use of smoke screens and listening devices on ships helped in identifying submarine positions. These technological advancements marked the beginning of more sophisticated anti-submarine warfare strategies.