The four years of conflict from 1914 to 1918 altered Langevin’s scientific focus in two ways. First, he had to set aside the international network of scientists. Second, he applied his talents to support the French war effort. Following encouragement from Jean Perrin and Marie CurieCurie, Marieencourages Langevin, he developed a proposal from the Russian émigréConstantin Chilowsky Constantin Chilowsky for underwater ultrasonicUltrasonicssubmarine detection detection and communicationUltrasonicscommunications. Supported by Victor ColinColin, Victor and Marcel TournierTournier, Marcel, by the end of 1915 they had demonstrated that a beam of ultrasound at 100 kHz could be created using a singing condenser. Reception used an underwater microphone. Langevin also developed a new means of measuring ultrasonic poweUltrasonicspowerr, the torsion balanceTorsion balance. The project moved to the Naval Dockyard in ToulonToulon, where Tournier detected the first ultrasonic echoes in June 1916. Chilowsky left, but not before filing a patentPatentcapacitive transducer in their joint names.