device which picked up radio signals from a U-boat while it 

 was transmitting by wireless and indicated the U-boat's 

 direction,, Installed at first at shore stations and later on 

 escort vessels, E/F D/F proved most helpful in giving warning 

 of a submarine in the vicinity. Two or more sets of the de- 

 vice could be used, by triangulation, to locate the general 

 position of a U-boat. 



Also s late in 1940, radar began to be installed, first 

 on ships, then on aircraft,. Radar enabled the bearing and 

 range of the target to be determined, even at night or during 

 conditions of poor visibility = 



During the nine months of Period II, 23 German U-boats 

 were sunk or probably sunk in the Atlantic and eleven Italian 

 submarines in the Mediterranean, 



To offset these losses, the Germans had commissioned 

 about 45 new submarines, giving them an estimated 54 U-boats 

 available at the close of the period, or about twice the 

 number they had at its beginning. Despite the greater allied 

 anti-submarine effort, the average life of a U-boat at sea 

 had risen from the three months of Period I to four months, 

 and the average U-boat sank per month 4 ships of 22,000 

 gross tons, a slight increase in tonnage over the previous 

 period. The merchant ship U-boat exchange rate, however, had 

 swung slightly in the former's favor with 16 ships of 88,000 

 gross tons sunk for every U-boat sunk or probably sunk. 



From the point of view of available shipping, the Allies 

 were deeper than ever in the red Total shipping losses of 

 456,000 ?ross tons per month represented an increase of nearly 

 60 per cent over the first period. The building rate of ships 

 had" increased to onl:^ 114,000 gross tons per month, so that 

 the net loss brought total shipping available down from about 

 38,000,000 gross tons at the start of the period to about 

 35,000,000 gross tons at the period's end* 



The British anti-submarine fleet received an important 

 addition during the period* In return for the right to lease 

 bases in British Western Eemi sphere territory like Newfound- 

 land, Bermuda and Trinidad, the United States transferred to 

 the British fifty old-type destroyers. 



