ABSTRACT
As fear of a fifth column grew, the US government began to close German and German-American news agencies, travel concerns and other businesses, all of which were believed to be part of a vast network of spying and information gathering for Berlin. While the latter destroyed US ships, in the Atlantic-Caribbean the U-boats came close to severing the vital lifeline to Great Britain as well as nearly crippling the US war industry by cutting off the supply of raw materials. 'It can be argued', writes a student of submarine warfare, 'that the Allies could have lost World War II if the U-boat had not been defeated by mid-1943'. There was an extraordinary English intelligence coup breaking the U-boat codes, the Enigma, through a cryptoanalysis operation called 'Ultra'. Operation 'Ultra' has been called 'the greatest secret in World War II after the atom bomb.'.
