Twenty Thousand Leagues Under the Sea
by Jules Verne

Captain Nemo and his crew sail around the world on a mission to end war among the surface nations. Predicting nuclear submarines and world war, Jules Verne’s classic is well worth a second (or first) read.  I first read it when I was about ten, having bought a tiny little paperback version at the grocery store for 25 cents.  You can download it free at Manybooks.net.