 In particular, this was because most of the ships sunk by U-boats were not in convoys, but sailing alone, or having become separated from convoys.At no time during the campaign were supply lines to Britain interrupted; even during the "Bismarck" crisis, convoys sailed as usual (although with heavier escorts).In all, during the Atlantic Campaign only 10% of transatlantic convoys that sailed were attacked, and of those attacked only 10% on average of the ships were lost.