From the end of 1942 onwards more and more planes and vessels were outfitted with the new and more sensitive centrimetric radar.
This truly spelled doom for U-Boats...even the periscope of a submerged U-Boat could be detected from a considerable distance...
Before that they used much less sensitive sensors, metric radar and even cruder sets.....
One of these sets lit up U-100 before it was rammed and sunk and allowed the cruisers HMS Norfolk and Suffolk to keep track of the Bismarck during its sortie.
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Daddy cool 
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