U-boats initially gained an advantage by entering a convoy on the surface at night and attacking from among the merchant ships. British analysis, including work by Wrens, identified the pattern. Experienced commanders in trawlers, sloops, or corvettes could then be positioned inside the convoy to meet a submarine that believed it had reached easy targets. The resulting change in losses could look like a mysterious new technology, although tactical understanding had actually turned the U-boat's own method into a trap. Periscopes and torpedo wakes remained difficult to see in darkness.
Chapter · 2:50:25-2:54:46
Night convoy defence could turn a U-boat's tactic against it
The convoy discussion shows how escorts learned to exploit U-boats entering the convoy at night instead of treating every contact as a technological mystery.