1914 - (April 27) Reginald Fessenden, of Submarine Signal Corporation, used a Fessenden Oscillator to reflect a signal off an iceberg and simultaneously reflect an acoustic signal off the sea bottom.
1919 - French scientists succeed in running the first line of soundings obtained from an acoustic echo sounder.
1922 - The USS Stewart runs a line of soundings across the Atlantic Ocean using an acoustic echo sounder devised by Dr. Harvey Hayes.
1924 - The Coast and Geodetic Survey conducts the first RAR (radio acoustic ranging) navigation operations on the West Coast. This is the first navigation system capable of round-the-clock operation in all weather conditions, and does not require a navigator to see either some recognizable landmark or celestial object to position a vessel.
1934 - Edward Beebe is lowered in a tethered bathyscaph to a depth of 3,028 feet marking the advent of manned exploration of the sea.
1935 - Researchers at the Coast and Geodetic Survey invent an automatic telemetering radio sono-buoy.
1937 - Athelstan Spilhaus invents the bathythermograph, a continuously recording temperature measurement device.
1938 - Elliott B. Roberts, of the Coast and Geodetic Survey, develops the Roberts Radio Current Meter. This instrument is possibly the first automatic moored telemetering instrument to measure a physical oceanographic parameter.
1941-1945 - World War Two, inventions from this period pertinent to ocean exploration include deep-ocean camera systems, early magnetometers, sidescan sonar instruments, and early technology for guiding ROVs (remotely operated vehicles).
1954 - February 15, 1954, the French research submersible F.N.R.S. 3 dives to 13,257 feet off the coast of Dakar, Africa, piloted by Georges Houot and Pierre Willm. This ushered in the era of manned untethered research submersibles.
1955 - Tows the first marine magnetometer and discovers magnetic striping on the seafloor off the west coast