USS S-21 (SS-126) - USS S-21: First U.S. Gravity Measurements at Sea

USS S-21: First U.S. Gravity Measurements At Sea

The first U.S. gravity measurements at sea were made from the USS S-21 assisted by Eagle Boat 35 and Eagle Boat 58. After the first gravity measurements at sea had been made in 1926 from a submarine of the Royal Navy the Carnegie Institution proposed the U.S. take Caribbean Sea measurements using a gravimeter, or gravity meter, designed by Dr. Felix Vening Meinesz. Such measurements required the stability and lack of motion only attainable at sea on a submerged submarine. With assistance from the National Academy of Sciences, the U. S. Coast and Geodetic Survey, the U.S. Naval Observatory and U.S. Navy Hydrographic Office the expedition was arranged. Special chronometers necessary for the observations were furnished by the Naval Observatory. Dr. Meinesz accompanied the expedition with Elmer B. Collins representing the Hydrographic Office aboard S-21 with the Eagle Boats serving as tenders.

The route was from Hampton Roads starting 4 October 1928 and return by way of Key West, Florida, Galveston, Texas, Guantanamo, Cuba, the Virgin Islands and Puerto Rico with the return to Hampton Roads on 30 November 1928. The first of forty-nine gravity measurement stations was located at 36°56.7′N 76°19.19′W. The gravity measurements were accompanied by a sonic depth sounding with results published on a chart produced by the U.S. Navy Hydrographic Office. The gravity measurements were utilized in determining the shape of the Earth and of particular interest were the negative gravity anomalies. The results of this expedition, particularly the significant negative anomalies, created interest in a second expedition resulting in the Navy-Princeton gravity expedition to the West Indies in 1932 using the submarine USS S-48. That was in turn followed by a third measurement effort using USS Barracuda (SS-163) on the Gravimetric Survey Expedition.