Hi Visje

Bathytermograph is a device that measures an adiabatic magnitude.

An adiabatic magnitude is a physical magnitude that varies with respect to another vectorial one.

ie.: air temperature with respect to the altitude.

In this case it measures the variation of the temperature of the water in function of the distance from sea surface to the submarine (in function of the depth).

The temperature of the water diminishes smoothly with the depth. In some areas, to a certain depth, this diminution stops being smooth and it becomes abrupt.That certain depth line is called \"layer\", and doesn´t let pass and reflects the asdic waves. Any object under that layer (a submarine) is non-detectable by a surface hull mounted asdic (an escort).


As far I know the U-boats had no such device.

It would have been very useful for them in areas like the Arctic, where pronounced layers occur.

Best regards