Somebody pointed out that S.Ray's constant of the motion was actually stated in different notation about p.209 in Traite de balistique by Isidore Didion (French 2nd edition published 1860 is http://books.google.com/books?id=2C9LAAAAMAAJ) For long range battleship type gunnery, the Ray solution would be useless because the atmosphere gets exponentially thinner at higher altitude which should be a major effect that he can't handle. However, a perturbational analysis where the drag coefficient is regarded as small, start with the trivial parabolic no-drag solution then perturb it via series expansion... that still should be doable.