 With one exception later in the book, this is the last official communication from the U.S. Navy that "Nathan James" ever receives.While they can later surmise there must have been a series of major exchanges, as a simple, single exchange of 'counter-force' strikes would not account for the sheer scale of the fallout they later find, and they can also conclude other nuclear powers, like India, Pakistan, etc., have also fired at each other, the crew never learns with certainty what led to the launches or the exact sequence of events.Thomas then decides to head southward into the North Sea and then to the United Kingdom, in order to re-establish contact with friendly forces.