Possible Clues:

• German submarines in WW2
• Turnabouts in vessels
• It's about wandering on small crafts, which once sunk a lot of resources into the sea perhaps
• W.W. II threats
• Those who rarely put their head above water were part of major conflict in the sink business
• WWII threats
• Depth-charge targets
• Some subs
• German divers in American landing craft?
• German submarines