and 4 U-boats that stayed up and fought were sunk in April 1943 

 and 9 more in Kay, 



Also during the period, sonar gear was so improved that 

 U-boats could not escape out of range by deep submergence and 

 radio sonobuoys were first used during Period V. 



Durin~ the nine months of Period., V, a total of 168 enemy 

 submarines were sunk. Of these, 128 were German, IS Italian, 

 18 Japanese, and 4 Vichy French, 



The U-boats had made their extreme effort and lost. The 

 world-wide exchange rate as between merchant vessels sunk by 

 U-boats and U-boats sunk fell to three and a half ships to 

 one U-boat, one-third the rate of the previous period. The 

 efficiency' of U-boats fell to a new low* The average U-boat 

 sank oulv" about one half a ship of 3,200 gross tons per month 

 at sea, and the average life of a U-boat at sea was reduced 

 to approximately eight and a half months „ The expansion of 

 the U-boat fleet was definitely slowed down during the period 

 by the bombing of U-boat bases. The entire increase in German 

 U-boats available was only some fifty. 



Total shipping losses of Allied and neutral nations were 

 491,000 gross tons per month during Period V, or approximately 

 30 per cent less than during the preceding period, Meanwhile, 

 construction of new shipping, especially by the United States, 

 reached a new high of approximately 1,025,000 gross tons per 

 month resulting in a net monthly gain of about 535,000 gross 

 tons. For the first time during the war, shipping available 

 to the Allies increased, the increase during the period of 

 almost r <, 000, 000 gross tons bringing the level of total chip- 

 ping available at the close of Period V to approximately 

 30,500,000 gross tons, A highly satisfactory increase had 

 also been made in the number of ships available for ocean 

 escorts. The number grew from about 745 at the beginning 

 of Period V to approximately 950 by the end of June 1943, 

 The new ships included some 50 destroyer escorts and 25 

 escort carriers. 



Period VI: Through May 1944, 



Period VI of the antisubmarine war, from July 1943 

 through May 1944, saw the ITavies of the United States, Great 

 Britain, and Canada drive the enemy U-boats from the North 

 Atlantic 'envoy route and into a defensive position in which 



I o 



