Night Surfaced Attacks on Convoys
July 1940-March 1941
2.1 U-Boat Offensive
T>HE SECOND PHASE of the U-boat war was marked by a complete change in enemy tactics. The Germans, having discovered as a result of their high rate of loss that the U-boats were quite vulnerable to Asdic when submerged, decided to make use of the hours of darkness to regain their relative invisibility. At night, trimmed down on the surface, a U-boat offers a very small target to the human eye and is also rather difficult to detect by Asdic. The surfaced U-boat has the advantage of high speed and maneuverability and therefore has good chances of avoiding detection by the escorts. Acting on this principle and encouraged by the results achieved at night during the first period by a few of the more successful U-boat captains, the U-boats started, in July 1940, the general practice of attacking convoys at night from a surfaced position and then using their high surface speed to escape. Occasional daylight attacks were still made on ships sailing independently, and on stragglers from convoys.
Accompanying this change in enemy's tactics came the occupation of the French ports and their establishment as U-boat bases, marked by the first visit of a U-boat to Lorient on July 22. The use of French bases served to cut down the transit time of the U-boats and enabled them to extend their area of operations further westward in the Atlantic. From his air bases in France, the enemy was also able to send out long-range reconnaissance aircraft to pick up convoys in the Atlantic.
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