The average ship in a North Atlantic convoy took about 

 70 days to make a round trip, half the time being spent at sea 

 and half in port. This average ship of 6,500 gross tons could 

 carry about 8,000 long tons per trip Thus it took in 1943 a 

 fleet of between 7,000,000 and 10,000,000 gross tons merely 

 to keep the United Kingdom fed and supplied,, 



But we sent to Europe an Army, every soldier of which re- 

 quired the transportation of some 5 tons of equipment and 

 supplies when he went, and an additional ton for every month 

 he remained. Since complete replacements were needed on the 

 average once each year, that meant between 1G and 20 long tons 

 to maintain one soldier for a year, or 3 to 5 gross tons of 

 shipping which must always be available if he were to be con- 

 stantly supplied; in other words, a fleet of 20,000,000 gross 

 tons continually plying the Atlantic in order to keep 5,000,000 

 men in Europe, 



This was the logistical equation which had to be solved 

 with respect to the European and Mediterranean theatres . In 

 addition - though the Japanese threat to our ocean transpor- 

 tation was only a fraction of that on the other side of the 

 world - we still had many hundreds of thousands of soldiers 

 and sailors and marines in the Pacific who had also to be 

 supplied by sea with food and the tools of war, and over 

 routes far longer than those of the Atlantic „ 



The war against the U-boat, of which the Battle of the 

 Atlantic was the major action, illustrated, as did perhaps 

 no other phase of World War II, how close - in this era of 

 science and scientific weapons - is the interplay between the 

 experimentation of the research worker in his laboratory and 

 the tactical planning of the military leader in his theatre 

 of operations,. 



The anti-submarine war divides itself naturally into a 

 number of chronological periods each marked by a typical 

 homogeneity of U-boat strategy and tactics and of Allied 

 countermeasures . 



Period I . 



Period I extended from the beginning of the war through 

 June 1940 , 



The German invasion of Poland, 1 September 1939, which 

 marked the outbreak of World War II, found the Germans with 



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