Other advances in underwater acoustics included the development of acoustic mines. The development of both active ASDIC and passive sonar (SOund Navigation And Ranging) proceeded apace during the war, driven by the first large scale deployments of submarines. Pioneering work was carried out during this time in France by Paul Langevin and in Britain by A B Wood and associates. Between 19, a number of echolocation patents were granted in Europe and the U.S., culminating in Reginald A. Systems for detecting icebergs and U-boats were developed.

The sinking of Titanic in 1912 and the start of World War I provided the impetus for the next wave of progress in underwater acoustics. In 1877 Lord Rayleigh wrote the Theory of Sound and established modern acoustic theory. The result they obtained was within about 2% of currently accepted values. They measured a sound speed of 1435 metres per second over a 17 kilometre(Km) distance, providing the first quantitative measurement of sound speed in water. In 1826, on Lake Geneva, they measured the elapsed time between a flash of light and the sound of a submerged ship's bell heard using an underwater listening horn. The next major step in the development of underwater acoustics was made by Daniel Colladon, a Swiss physicist, and Charles Sturm, a French mathematician. In 1687 Isaac Newton wrote his Mathematical Principles of Natural Philosophy which included the first mathematical treatment of sound. The science of underwater acoustics began in 1490, when Leonardo da Vinci wrote the following, 'If you cause your ship to stop and place the head of a long tube in the water and place the outer extremity to your ear, you will hear ships at a great distance from you.' Underwater sound has probably been used by marine animals for millions of years. 4.1 Comparison with airborne sound levelsДЄ seafloor map produced by multibeam sonar.

2.2 Speed of sound, density and impedance.

2.1 Sound waves in water, bottom of sea.

Water and soundwaves