regarding the Huff-Duff, which as someone correctly stated was HF-DF, or high frequency- direction finding, my understanding is that as well as shore stations being able to DF, convoy escort vessels could also DF. Presumably since they were much nearer the target ( the U-Boat ) it would be more accurate, but since the convoy vessels would be relatively close together, it would only give them a direction line rather than a position.