The bathythermograph, or BT. was developed prior to WWII to measure temperature profiles in the open ocean, while underway, for ocean surveying. It became invaluable during WWII to allow estimation of sound speed profiles and calculation of sonar ranges, for antisubmarine warfare from surface ships.
The really interesting history of the BT is attached.
It was not superseded until the development of an expendable BT (XBT) in the early 1960's (I got to use one of these first in 1967); but by the early 1970s there were more XBT profiles than BT profiles being taken, all from ships crossing the oceans. The ships, however, were a problem; they were expensive to operate, and did not go all the places from which you wanted to have profiles. The work of global coverage of the oceans with profiles of temperature and salinity (and today, also including biogeochemical instruments) is now done by autonomous profiling floats (robots!) called Argo; no ships except to put the floats in...they drift around with the large ocean currents. The project started in 2000, is international, involves about 80 floats being deployed each year, each lasting about 5 years. The data are radioed by satellite back to shore stations.
It all started with the BT.
The really interesting history of the BT is attached.
It was not superseded until the development of an expendable BT (XBT) in the early 1960's (I got to use one of these first in 1967); but by the early 1970s there were more XBT profiles than BT profiles being taken, all from ships crossing the oceans. The ships, however, were a problem; they were expensive to operate, and did not go all the places from which you wanted to have profiles. The work of global coverage of the oceans with profiles of temperature and salinity (and today, also including biogeochemical instruments) is now done by autonomous profiling floats (robots!) called Argo; no ships except to put the floats in...they drift around with the large ocean currents. The project started in 2000, is international, involves about 80 floats being deployed each year, each lasting about 5 years. The data are radioed by satellite back to shore stations.
It all started with the BT.