Why did the Japanese expect the United States navy would attack the Home Islands?

The japanese was in their best military moment. Great army, great expansion, victory over victory. The famous "banzai", even their own government believe in their invencibility. The UK was withdrawing, China invaded, Holland asiatic islands invaded, Only Soviet Union could stop them.

In addition, Japanese Navy was in their best moment, really impressive even better than german navy. For the Japanese, USA had the only navy that could defy his expansions plan. Pearl harbour was a careful plan in order to give USA a heavy knock in order to prevent Americans any danger in their desires to make a great empire. However, the knock ended in great fail because the US carriers werent there. The Surprise Japanese attack didnt have the effect that they expected and provocked "the wake of the US Giant navy" the only enemy with the power to defeat them was awake.

"Creating a battle plan that depends on the enemy's cooperation is a beginner's mistake."

They did not have any shortage of such mistakes.

They fought Midway with the expectation that the US carriers wouldn't show up until they took the island. That's why their entire fleet was armed with land attack armaments at the time the USN showed up, and Nagumo ended up having to waste 30 minutes rearming his bombers, costing him the battle.

They fought Guadalcanal because they expected Nimitz to only send 2,000 men and planned accordingly. Ichiki's initial detachment consisted of less than 1,000 men, and despite being repulsed, they sent Kawaguchi's Brigade of 3,500. Only after that was repulsed did they finally decide to send a whole Division. To compare, Nimitz's initial force was the first Marine Division at 10,000, with actual heavy weaponry and supplies, something the Japanese couldn't transport onto Guadalcanal.

They were utterly unprepared for Saipan (The entire Marianas had only 50 land-based aircraft then) because they hoped the United States would attack somewhere else instead. Admiral Ozawa was the only one that thought otherwise (which is why he even had a battle plan drawn out that resulted in the battle of the Philippine Sea).

One myth is that the Japanese only lacked material. They lacked far more than that, especially in the department of employed strategists. It's enough to write two books on, so I'd recommend you pick up a full biography of Tsuji Masanobu, and take special note on what kind of education he received and how much battle experience he had before starting to command entire armies by proxy (spoiler: near 0).

Kindly allow me to update completely.

As a starter, I being a native speaker, kindly be reminded it would sound very strange when the OP says "Kantai Kessen, the Japanese naval strategy for a Pacific war" ( Excluding the fact that the Wiki was updated by someone ). The reason is, simply, in term of the usage of the word. Kantai Kessen simply denotes the one time battle. If you tell me the reason why, then I will have to escape to say, "Please learn Japanese"....... Had I been heard as a Kantai Kessen Shugi, since the last word means kind of like a motto or, more like, considering the atmosphere at that time in my assumption, it would be more like a "belief or faith" ( in terms of like religions ) into large scale battleship classes ( such as Yamato class ) using the main weapons in order to gain the "decisive win" as the Wiki says also.

So in the perspective of gaining "decisive wins or victories", the term "Kantai Kessen" can be applied to any battle, from Midway to Leyte to even Yamato's de facto Banzai attack into Okinawa.

Now I am afraid to say, the OP's question is not so well understandable to me.

I would like to assume the OP has some doubt about the below line of the Wiki.

This would limit the time the American fleet could operate in the western Pacific and force them to commit to a single major battle, a battle which Japan could win decisively as they had at the Battle of Tsushima.[5]

Now regarding this issue, I found a site which is in Japanese. So if you have doubt in your mind that mine quote and its corresponding translation would be wrong, please go to Japanese Language site for the check.

This site explains,

( Why does this site allow the citation of Chinese characters?? ) --> So that I can not cite the original text.

Granted the above site explains, the top officers' strategy at the initial stage was

1 Strike and push eastward to "destroy" or gain the "decisive victory" in the pacific sea.

2 Win at any cost and destroy anywhere in the Pacific Sea the U.S navy. This thought itself became the object of the war. ( = meaning, or suggesting, the Imperial Japanese Navy did not have "logical" strategies in their minds.

And this site which is fortunately in English, could become a very important answer to the questioner.

Zettai Kokubo Ken, Absolute National Defense Zone, which was drafted around early 1943 when the tide turned unfavorably to the Japanese Imperial Army, set the literally "to set the definite lines or perimeters into which American army should not have been allowed" ( in order to evade the bombardment by the U.S airforce on the homeisland.( For example, let us examine the Battle Of Iwo Jima, which was one of the most fiercest fights between the JPA and the U.S during the pacific war. Almost everybody, around 18,000 men died. The U.S casualty was also hideous, around 7,000 men died. The reason why the JPA fought so hard? Simply in order not for the U.S to set up the airbase for their bombardment )).

So that the O.P's question, was contrary to thoughts of the then high ranking officers of JPA. I could be able to say, the JPA actually had no systematic plan in its principle after all.

I hope I could have answered to the questioner's question somehow.

Have a happy day.

The Japanese navy had a fundamental misunderstanding of the American navy, in large part because of its experience with other, European navies such as those of Russia and Britain. And perhaps they were confused by America's War Plan Orange," which preached similar doctrine, but was more "honored in the breach than the observance."

In the 1905 war with Russia, that country had a (Far East) naval base at Port Arthur, Manchuria. The Japanese won the naval war by defeating the Russian fleet there, and then winning a second battle at Tsushima Straits against a reinforcing fleet headed to Port Arthur, and took the most obvious route there. Likewise, the Japanese destroyed a British task force that was detailed to defend Singapore and Malaysia.

The Japanese thinking had some merit for the Japanese Empire up to about 1920, which included the Home Islands, Iwo Jima, Okinawa, Korea, Formosa, and a bit more. But the 1920s and 1930s militarization of the islands (Marianas, Caroline, and Marshals) acquired in the South Pacific Mandate after World War II (which specified de militarization) made it very dangerous to for the Americans to leave these islands in the rear during a "main force" strike. Also, during the 1930s, "dissidents" in both the American and Japanese navies opined that advances in air and submarine warfare had made such "main force" naval tactics obsolete. The difference was that America eventually allowed its dissidents to prevail, and Japan didn't.

And when World War II began, Japan began expanding far beyond what original plans envisioned, including to Papua New Guinea in the south, Midway Island to the East, and the Aleutian Islands in the Northeast. With a huge bubble of that sort, the Americans found through trial and error that a more expeditious strategy than its original Plan Orange was to "pick off" Japanese forces along the perimeter (as they did at Coral Sea, Midway, and the Aleutians), instead of trying to fight the main Japanese navy near the Home islands. Eventually, the Americans did "get there," but only after the Japanese navy had been greatly weakened by attrition.

In sports terms, the Americans used a "full court press" over the whole Pacific, fighting a series of "duels" that would deplete Japanese naval power at a faster rate than American naval power. In this regard, they were using an "attrition" strategy like that of U.S. Grant against Robert E. Lee. (During the course of the war, the Americans outbuilt the Japanese 3 to 1, and that's not counting the material they used against Hitler.) The Japanese were hoping that the Americans would send their fleets against the Japanese fleet for one all out battle after another, and that the Japanese would destroy three or four American fleets in the process without losing her own.

The Americans preferred to bleed the Japanese to death by "trading shots." Coral Sea, one Japanese carrier sunk, two put out of action, versus one American carrier sunk, one damaged (the Yorktown, repaired for the Midway battle in one weekend). At Midway, the Americans sank four carriers while losing one, but that hardly mattered; a four to three "kill" ratio would have been sufficient. Basically, the Japanese would have had to sink all three American carriers with the loss of no more than one to maintain the 1 to 3 parity dictated by the countries' relative productions. Anything "worse" (e.g. two Japanese carriers lost for three Americans), and the Americans would win.

Put another way, the Japanese (reasonably) believed that the Americans would follow a "script" laid down by the Russians, British, and the Americans themselves. The Russian navy at Tsushima in 1905 followed essentially the same tactics after the surprise attack at Port Arthur as before (even to the point of using the route the Japanese expected them to). This British didn't seem to care that they could "lose the war in one afternoon" at Jutland in 1916. But the Americans departed from a script of one "all or nothing" battle when their numerical superiority could make the "law of averages" work for them in numerous "knife fights." Give credit to Admirals Halsey, Nimitz, and others for that.