During the last year of World War II the once surface-bound diesel-electric U-boat ushered in the age of 'total undersea war' with the introduction of an air mast, or 'snorkel' as it became known among the men who served in D nitz's submarine fleet. U-boats no longer needed to surface to charge batteries or refresh air; they rarely communicated with their command, operating silently and alone among the shallow coastal waters of the United Kingdom...