Given the time lag, Beck figures he can get away with giving this one a half-assed try. He really should swing round and approach the wreck on the surface, which would get him there faster, but which would be nearly suicidal. So instead, he closes the hatches and descends to periscope depth as he draws closer. This cuts the U-boat’s speed to a crawling seven knots, so it takes them about three hours to get back to the atoll of bobbing brown bales that marks the site.