However , the development of the destroyer and aircraft with a longer patrol range were effective at countering the U-boat threat .
The Germans hoped to sever the vital supply lines between Britain and America , sinking many tons of shipping with U-boats , German submarines .
The development of the destroyer and aircraft with a longer patrol range were effective at countering the U-boat threat .
The Germans hoped to sever the vital supply lines between Britain and America , sinking many tons of shipping with U-boats , German submarines .