Hi, rechecked my copy of Blair's "Hitler's U-Boat war".
1. seems to have depended on the Skipper. By this time, the bay of Biscay was a very dangerous place with high Allied air coverage. Since Coastal Command ACs were equipped with radar and Leigh lights, surfaced U-Boats were never safe. At night, the sound of ACs was drowned out by the U-Boast diesel. U-Boats preferred travelling on the surface during the day because it was easier to spot ACs from a longer range. Seems that they would have generally traveled on the surface at higher speeds to get through the Bay faster;
2. U-Flak, it was from about june to october 43. The U-Flak escort concept was given up quickly because it just lead to increased U-Boat losses;
3. normal speed. Again depends, best fuel economy speed was using one engine only, 6-7 knots, but that was generally only used when they wanted to stretch range to the limit, for example patrols by VIIs to the U.S. East Coast when they did not have access to U-Tankers. Normally for mid-Atlantic patrols, they would follow orders from U-Boat Control which would often switch them to new patrol zones. Normal cruising speed in the mid-Atlantic was probably more in the 10-12 knots range.
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