[Ducimus]

Originally Posted by Seeadler

You're correct, the German U-boats had no bathythermographs. They knew that these layers existed, but could not determine whether there is a termal layer in a given depth or if the boat is below or above a thermal layer.

Originally Posted by TarJak

One of the factors that drove the lack of German advance in this area was the fact that in the Atlantic where most of their submarine ops took place, the thermal layers were commonly deeper than the subs were capable of diving anyway.

That's not to say that is true in all locations or conditions, just the most common conditions in the Atlantic.

QFT