On the other hand, in convoyed shipping, speed was the signif- 

 icant factor only in the presence of an air escort. 



Another striking result which emerged from the study was 

 that the number of ships sunk in a convoy was on the average 

 independent of the convoy's size so long as the number of es- 

 corts was the same. This meant that large convoys would in 

 the long run lose a smaller percentage of ships to U-boat 

 attacks and at the same time there would be a saving in the 

 use cf escorts. 



The effectiveness of Allied aircraft drove U-boat com- 

 manders to adopt a system of complete submergence during the 

 day time, which robbed the submarine of its mobility. 



On the part of the Germans, the most revolutionary tech- 

 nical development of Period VI was the fitting of Schnorchel 

 to U-boats . The first U-boats were fitted with Schnorchel in 

 February of 1944 . 



Improvements to Allied sonar gear came into service use 

 about this time and enabled sound gear operators to determine 

 the bearing and location of targets with much greater accuracy 

 and rapidity. Several improvements in depth charges also came 

 into use on American ships about this time. 



All these various advances in equipment, weapons and tac- 

 tics brought about the sinking or probable sinking of 21 U-boats 

 per month during the eleven months of Period VI. Of the total 

 of 234 U-boats destroyed, 199 were German, 28 were Japanese 

 and 7 were Italian,, During the period, the Allied and neutral 

 nations lost an average of 1G4,000 gross tons cf shipping per 

 month from all causes, or about a third as much as during the 

 preceding period. At the same time, the construction of new 

 merchant shipping Increased to approximately 1,100,000 tons 

 per month, making a net gain of 976,000 gross tons per month. 

 The total increase of nearly 11,000,000 gross tons made avail- 

 able to the Allies at the end of Period VI, approximately 

 7,500 ships, totaling 47,500,000 gross tons, of which 10 s 500,000 

 gross tons consisted of tankers,. 



Period VII: Through August 1945, 



Period VI I s the final phase of the U-boat war, extended 

 from June 1944 to the surrender of Germany on 8 May 1945 and 

 the capitulation of Japan on 14 August 1945. 



78 



