the opposing fleets would precede the final surface battle, they increasingly considered the enemy's carriers as the main targets of naval air power. Hence, in the early 1930s, the Imperial Japanese Navy adhered to no unified doctrine as to how carriers would be utilized in a fleet action and had no clear vision as to the role of air power in naval warfare. But with the continued increase in the range and power of aircraft, carriers became acknowledged for their ability to strike at targets beyond the range of surface guns and torpedoes. Including gunnery staffs as well as naval aviators, the IJN became convinced that carrier aircraft should be used for a preemptive strike against the enemy's carriers to achieve air superiority in the proximity of the surface battle. Around 1932–33, the IJN began to shift its aerial focus from targeting the enemy's battleships to their aircraft carriers; and by the mid-30s, with the improved performance of bombing aircraft and particularly dive-bombers, the destruction of the enemy's carrier force became the primary focus of Japan's carrier forces. The emerging concept of a mass aerial attack also shifted the emphasis away from the protection of the main battle fleet to attacks on targets over the horizon. Essential to the implementation of such a tactic was the locating of the enemy before the enemy found the Japanese carriers. As a consequence, it was important to the Japanese that naval aircraft be able to "outrange the enemy" in the air, just as Japanese surface forces could do by naval gunnery and torpedo attacks. Subsequently, throughout the 1930s, Japanese naval aviation emphasized range in its specifications for new aircraft. Land-based air groups In addition to developing carrier-based aviation, the IJN maintained many land-based air groups. In the early 1930s, the Japanese created a new category of aircraft termed rikujo kogeki-ki (land based attack aircraft) or Rikko for short. This was in keeping with the strategy of providing a rapid defense of the home islands against the possible westward advance of an American naval offensive across the Pacific. Land-based aircraft actually provided the bulk of Japanese naval aviation up to the eve of the Pacific War. In this regard, Japan was unique among the three major naval powers during the interwar period and the immediate prewar years with only the two air wings of the US Marine Corps being analogous to Japan's land based