Period III . 



April 1941, when the sub-surface warfare group of 1IDRC 

 was just getting under way, narked the beginning of the U-boat 

 war's third period, which was to Inst until December 1941 



Once again. Allied countermeasures had forced the Germans 

 to switch tactics and Period III saw a shift from the close 

 surface attack by one or two U-boats in favor of the "wolf 

 pack" system, in which a U-boat encountering' a convoy withheld 

 its attack until it could summon other submarines in the vicin- 

 ity for an attack in unison. 



One reason for the change in tactics was the increasing 

 effectiveness of Allied escort vessels equipped with the High 

 Frequency Direction Finder and radar,, 



Another reason for the adoption of the "wolf pack" system 

 was that, because of deaths due to Allied action and to the 

 expansion of the U-boat fleet, seasoned submarine officers and 

 men were being spread thinner and thinner. The "wolf pack" 

 attack in concert enabled less experienced U-boat crews to be 

 guided by their more experienced colleagues 



April 1941 opened with an attack which was to be typical 

 of the next 9 months , when five U-boats combined forces to 

 raid convoy SE-26 before its escort had joined up. Ten ships 

 of the convoy, including an armed merchant vessel, were sunk, 



U-boats began pushing the principal areas of their 

 attacks farther southward and westward to the Azores and Free- 

 town area, June 1941 saw the area of attacks still spreading 

 with U-boats raiding off Newfoundland ard south of Greenland . 

 The U-boats' score for the month was 57 ships of 296,000 

 gross tons. During the month, however , 5 U-boats were sunk,, 



The spread of the U-bcat war caused President • Roosevelt 

 to announce in July 1941 that the safety of the United States 

 required the basing of American anti-submarine forces In 

 Iceland, The Allies reached a decision that the only means 

 of safeguarding convoys ""as to provide an escort clear across 

 the Atlantic , even though this meant diminishing the number 

 of escort vessels which could be assigned to each convoy. 



The Allies could find some satisfaction in statistics. 

 In September 1940, with an average of only 7 U-boats at sea. 



