By 1968, North Vietnam had grown extremely proficient at defending its airspace against American warplanes, so the Navy turned to a platform Hanoi would find far harder to destroy, and whose shells cost far less than bombs and missiles. USS New Jersey's 16-inch Mark 7 guns could hurl one-ton shells more than 20 miles, and unlike aircraft, she could stay on station and respond to fighting as it unfolded. She supported the 1st and 3rd Marine Divis…