The guiding ideology of < gradually reducing the challenge > and (nine-stage tapering operation) should be said to be consistent. After Japan and Russo-Japanese War, Japan regarded the United States as the most important imaginary enemy threatening Japan's sea power. Because the American navy is stronger, Akiyama Makoto and Sato Tetsuzaburo formulated the so-called "gradual reduction" strategy of the Japanese navy to the United States. Among them, Sato Tiesaburo put forward three foundations: the theory of 70% military power against the United States, the theory of gradually shrinking to meet the attack and the theory of decisive battle of the fleet. (The specific background and content of this strategy are not detailed here. These three foundations can be regarded as three steps: "70% military strength against the United States" was obtained by Sato and Akiyama through cooperative research, which is the premise of the gradual reduction strategy and the guidance of naval armament construction. Mahan's theory holds that "the standard of a country's armament should be able to cope not only with accidental dangers, but also with the most terrible dangers". Therefore, its standard is the predictable strength that a country can assemble relative to the strength of the strongest imaginary enemy country. Therefore, Japan's naval armament must be planned according to the overall strength of the US navy (at that time, the Panama Canal was under construction, and Sato and Akiyama considered this factor). In this regard, the two of them put forward a formula: from a strategic point of view, the offensive side needs to maintain an advantage of more than 50% over the defensive side, that is, the offensive side: the defensive side is 1.5: 1, on the contrary, the defensive side can meet the defensive requirements as long as it can reach 70% strength. In Sato's definition, the Japanese naval fleet is a strategic defensive fleet, and it is a fleet specially used for defense (special defense is a Science of Tactics concept, which refers to the defense of a certain area, similar to the defense in basketball), that is to say, the armament of the Japanese navy should maintain 70% of that of the US navy. The theory of "decreasing to meet the challenge" is the means of decreasing strategy and the guidance of combat tactics. Its core idea is that because the American fleet is too strong, it should choose the strategy of attacking the enemy after. When the decisive battle is postponed, the main force will hide in the snow. Before that, the American fleet will be consumed by auxiliary forces, and the decisive battle will be held when the Japanese navy can accept it. The so-called "fleet decisive battle theory" is the idea of deciding the outcome of the war through the decisive battle between the main fleets of the enemy and ourselves. This is the purpose of the reduction strategy. It has two origins. Its theoretical origin comes from Mahan's influence on Sato and even the whole Japanese navy. In his masterpiece On Sea Power, Mahan strongly advocated that the purpose of wartime troops was to defeat the enemy fleet and master the sea power. The origin of the experience was the decisive victory of the Japanese navy in the Sino-Japanese War of 1894-1895, especially the subsequent naval battle against Malaysia. Therefore, it should be said that "gradually reducing to meet the challenge" is part of the above-mentioned whole operational thinking. Of course, "gradually reducing to meet the challenge" can also be regarded as a "gradually reducing" strategy. Judging from this development, in addition to the so-called "August 8th Fleet" (2 battleships, each with 8 battleships; Two first-class cruisers, each with 8 first-class cruisers; 2 second-class cruisers, each with 8 second-class cruisers; Three mining teams, each with 12 destroyers. However, this strategic plan has encountered problems in its implementation, which is the famous "Naval Disarmament Conference". The plan of Japan's "August 8th Fleet" was disrupted. Looking at it again, it should be said that it is a specific operational plan in adjustment. It was also formulated under the strategic idea of "gradual reduction". Originally, the Japanese navy's idea of a decisive battle with the United States was to assemble the main force of the fleet in the waters near Amami Island, and then go out to the waters east of Honshu Island to launch a "torpedo war on the ocean" to fight the fleet. In the Taisho era and the early Showa period, this idea basically didn't change much except to move the decisive battle site to Ogasawara Islands. After the London Conference, the Japanese navy's plan to expand auxiliary warships was aborted, so it was further decided to expand the battlefield to the central and eastern Pacific Ocean and launch a surprise attack immediately after the US fleet left its home port. The product of the constant revision of this concept is the so-called "nine-stage operation" plan.

The "nine-stage operation" assumes that the US Pacific Fleet and Atlantic Fleet are roughly divided into two groups after the war. One group is an Asian fleet with light cruisers as the main force, which should start from the Philippines. For this fleet, Japan is scheduled to deal with the third fleet, which is also dominated by light cruisers. Another American fleet, the Pacific Fleet reinforced by the Atlantic Fleet, is expected to depart from the west coast of the United States or Hawaii and will be divided into four groups: one group of submarines will launch a war against Japan; The other group, with 4 to 6 heavy cruisers as the main force, will engage in surprise attacks and harassment tasks; The third group, with 14 heavy cruiser as the main force, will serve as the pioneer and reconnaissance mission of the main fleet; The last regiment, with the 15 battleship and several aircraft carriers as the main force, took on the main force of fighting against Japan.

In fact, the Japanese divided the battle with the American fleet into nine stages: the first stage started from the west coast of the American fleet and reached Hawaii. After that, the American fleet will occupy part of the Marshall Islands as a bridgehead. The voyage of the US fleet after its departure from Hawaii was designated as the second leg, and the voyage before its occupation of the Marshall Islands was the third leg. After the US fleet occupied the Marshall Islands, it will reach the western Pacific called the "Inner South China Sea", which is the fourth voyage. The American fleet attacked from Marshall Islands until it reached the predetermined area of Japan near Caroline Islands. This distance is divided into the fifth and sixth segments. The eve of the scheduled decisive battle is the seventh stage, the dawn of the scheduled decisive battle day is the eighth stage, and the final fleet decisive battle is the ninth stage of the war.

The plan of the Japanese navy is that all the fleets will be assembled by trucks in the Caroline Islands within 72 hours after the war, and use this as a forward base.

With the passage of time, the forces required for the ninth stage of operations have also changed. Take 1936 as an example, the nine-stage battle plan of the Japanese navy after it entered the "treaty-free era". The plan predicts that 1946 will see the outbreak of war against the United States. At that time, the first and second stages will be monitored by two reconnaissance cruisers, three 2800-ton "flagship submarines" and 27 1900-ton ocean-going forecourt respectively. The troops required in the third to sixth sections are four "super warships", four "Ruihe" aircraft carriers, 1 reconnaissance cruisers, two "flagship submarines" and 18 "Haida" submarines with 508 mm 12 guns. The third and fifth paragraphs will be attacked by the submarine Haida, and the fourth and sixth paragraphs will be attacked by carrier-based aircraft and land-based aircraft respectively. In the seventh stage on the eve of the decisive battle, the Japanese navy will launch a night attack with a huge torpedo force consisting of 4 submarines, 28 cruisers and 64 destroyers; In the early morning of the next day, the eighth leg was supplemented by 10 submarine and carrier-based aircraft. In the ninth stage of the final battle of the fleet, 10 battleship, six aircraft carriers and 10 submarine will be used to make a final blow to the main fleet of the United States.

It should be said that "gradually reducing to meet the attack" and "nine-stage operation" are the same operational guidance under the same strategic thinking. "Nine-stage operation" is the embodiment of "gradually decreasing to meet the attack".