On the other side of the ledger, however, toward the close 

 of Period IV, Allied aircraft were beginning to prove themselves 

 more and more important as detectors and attackers of U-boatSc 

 Allied planes were equipped with improved depth bombs filled 

 with charges of a new higher explosive Still more intensive 

 patrolling of the Bay of Biscay was undertaken „ Radar and 

 searchlights permitted Allied aircraft to extend their patrol- 

 ling into the night with excellent effect, though German tech- 

 nicians scored by developing a search receiver which could 

 detect transmission from Allied radar sets then in use 



Also, on the more optimistic side of the ledger was the 

 fact that Allied antisubmarine craft had been increased from 

 670 to 745, including 60 new destroyers and 12 auxiliary air- 

 craft carriers., The United States naval building program in- 

 cluded approximately 500 new escort vessels, of which about 

 half were destroyer escorts „ 



Another favorable factor was the tremendous gain in the 

 construction of merchant vessels, particularly on the part 

 of the United States, where the efforts of the Navy, the 

 Maritime Commission, the War Shipping Administration and the 

 American shipbuilding industry had pushed the rate of con- 

 struction up from 100,000 gross tons in January 1942 to 700,000 

 gross tons in September of that year 



Period V: Through June 1943 . 



The nine-month period from October 1942 through June 1943 

 marked the turning point in the war against the U-boat . 



The period's beginning saw the enemy submarines, driven 

 from American coastal waters, intensify their wolf pack tac- 

 tics against Allied shipping in the Atlantic, The early months 

 of the period saw Allied shipping losses mount to a new all- 

 time high But before this period of the war was over, inten- 

 sified Allied countermeasures and production had turned the 

 tide against the submarine,, 



Allied aircraft came into their own as an offensive weapon 

 against undersea raiders, American and British scientists 

 and technical experts forged so far ahead of the scientists of 

 the Axis that Admiral Doenitz shook up the whole German system 

 of technical development of submarine devices,, For the first 

 time during the war, new construction of shipping, particularly 



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