I agree with Rogissimo
I cannot see anyway one can use the solutions to 5 and 9 to get the theme, especially 5d.
I am pleased to say that I have now finished though I 'm not happy with the clue for 16d or the clue for 15ac. In the case of the latter clue I think the word should be America, not American.
I can say that my FOI was 5d, LOI was 15ac. My CODs possibly 8ac, though I didn't know the battle, 18d and 4d. I'm not totally happy with the clue for 17ac either, or the parsing for 13d. Come on Paul - tighten up.