Advices: If you have to dive your boat to ocean floor

[Heibges]

From the Uboat Commanders Handbook:

57.) As regards the condition of ASDIC in relation to the transmitting capacity of the water, it has been ascertained that the efficiency of the submarine-detecting gear is considerably reduced in sea areas with numerous layers of water.

a.) Formation of layes of varying density ("stratification") of the water of the sea occurs after a long spell of sunshine on a calm sea, and also in a high degree in places where there is a mingling of different types of water.............. Continual observation and measuring of water densities and temperatures are therefore important and indenspensible, for establishing the presense of "stratification" when submerging to considerable depths as a means of evading pursuit by position finding.

b.) In additon, position finding is very difficult, and almost impossible, in shallow water of varying depths (sand banks), where there are many wrecks, as well as in narrow bays (Norwegian fjords), as it is usually not an echo that is produced, but numerous echoes, which make it difficult to keep, but more especially to locate, the target.