Paul Kennedy reports that in World War I, when the Japanese were allied with the UK, they patrolled the Indian Ocean at the request of Britain. They also "dispatched a dozen destroyers for anti-submarine work in the Mediterranean," he notes.
Nor did I know that in the German defense plan of 1938 called for it to build four aircraft carriers.
Finally, I learned that during World War II, more German U boats were sunk by Allied aircraft (288) than by surface ships (246). (Another bunch were deep-sixed by combined actions.)
Thomas E. Ricks covered the U.S. military from 1991 to 2008 for the Wall Street Journal and then the Washington Post. He can be reached at firstname.lastname@example.org.