The adversaries for U.S. Naval Aviators at the Battle of Midway and other notable air-sea battles of the Pacific War were aviators of the Imperial Japanese Navy. When the war began, they were an elite, experienced, battle-hardened group, having flown combat misions in the skies over China during the late-1930s. While some were commissioned officers, unlike in the U.S. Navy the majority of Japanese naval aviators were enlisted petty officers. As the war progressed, however, the Japanese policy of not rotating trained aircrews off the front-lines to train replacements, coupled with losses in air battles in the Solomon Islands, generally made for less skilled pilots in the cockpits of Japanese planes than existed in the war's early stages.