Exocets would just about bounce off the USS Iowa (class battleship) waterline armor.
There are other types of antiship missiles that dive from above. Battleship deck armor is considerably thinner than its belt armor. The 17-inch figure is the maximum thickness in certain limited areas. It's much less almost everywhere else.
The battleship thread comes up periodically on the sci.military.naval Usenet newsgroup. It's dismissed out of hand by the people there...many of whom have actual expertise in the field: active and former naval personnel, marine engineers, etc.
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I believe I said "next generation" exocet.