"Suppose, for example, that there is a secret convoy about to cross over from New York, and it contains thousands of troops, and some new weapon that will turn the tide in the war and save thousands of lives. And suppose that it is using a different code system, so that even after the Germans get our code books today they will not know about it. The Germans will focus their energies on sinking the convoys that they do know about—killing, perhaps, a few hundred crew members. But while their attention is on those convoys, the secret convoy will slip through and deliver its precious cargo and save thousands of lives."