The bathythermograph was invented by Althestan F. Spilhaus, of MIT's Metrology Dept. It was modified for WWII use in finding undersea sound corridors.  It is a small torpedo-shaped device with a temperature sensor and transducer that detects changers in hydrostatic pressure. It is dropped into the water to record pressure and temperature changes. Spilhaus also invented weather balloons, a device to measure air mass and wind direction.