I was trying to find a quote I remember from Clausewitz's On War and stumbled upon this site which has several books online, including On War and a few indexes, a copy of an unknown edition of Vom Kriege if you prefer German, a Clausewitz essay called Principles of War and Clausewitz in English: The Reception of Clausewitz in Britain and America 1815-1945.
Wow, I could spend weeks at this site.
I'm trying to accumulate as many ancient military texts as I can lay my electronic hands on and then post them here. I guess this is sort of like an early present on Christmas Eve. Enjoy.