1) Homer's Iliad, best translation
2) Homer's Odyssey, best translation
3) Shakespeare's Henry V. Cry Havoc and unleash the Dogs of War!
4) Tolstoy's War and Peace. Forgive the tedious Afterword about Napoleon and History.
5) George Bernard Shaw's Major Barbara. Superb wit, Andrew Undershaft is unforgettable.
6) C.S. Forester's Beat to Quarters. The Hornblower series starts with Mr Midshipman Hornblower but this is the first one I ever read and still the best. That said, they are all very much worthwhile.
7) Hemingway's Farewell to Arms--not a tale about a double amputee!. Also read The Sun also Rises.
8) Patrick O'Brian's Master and Commander. The whole series is terrific. I had the great pleasure of meeting O'Brian just before his death in 2000.
9) Tolkein's Lord of the Rings. Tolkein served as a Tommy during WWI and this book was written during WWII, for which it can be read as an extended metaphor (Sauron as Hitler, Saruman as Mussolini, the Eagles as the Yanks?).
10) George Macdonald Fraser. Flashman. The whole series is great for all history buffs. His autobiographical Quartered Safe out Here: A Harrowing Tale of World War II is also not to be missed.
I also met this author at a book signing at Hatchards in London before his death in 2008.