Disregard my email. I was trying to use F 5 for the the first letter and had to skip the black squares to make it work. Obviously was back solving. On reviewing my work I realized I should be using F 8, which was then consistent with the other coordinates. Great puzzle.
I just can’t get “you sank my battleship!“ out of my head now. Too many Saturday mornings watching cartoons (and the commercials that went with them). :-)