Southward advance spearheaded by Navy
It was the Imperial Japanese Army that played the leading role in the jingoism displayed from the Manchurian Incident through the Sino-Japanese War to the start of the Japanese-U.S. War.
The Army conspicuously took the lead in the conclusion of the Tripartite Pact, which is described as a point of no return leading up to the Japanese-U.S. War, and the advancement to northern French Indochina. But the Navy took the initiative in the advancement to southern French Indochina. What happened to the Navy, which had been consistently cautious about going to war with the United States?
When the Navy took a firm stand against the conclusion of the Tripartite Pact in the first Konoe Cabinet and the Cabinet of Kiichiro Hiranuma, those who advocated cooperation with Britain and the United States were holding the important posts, including Navy Minister Mitsumasa Yonai, Vice Navy Minister Isoroku Yamamoto and the Navy Ministry’s Naval Affairs Bureau chief Shigeyoshi Inoue.
But the numbers in the pro-German group increased among those under the section chiefs or lower ranks of the Navy Ministry. When Yonai assumed the position of Prime Minister, he also became a reserve admiral and when Yamamoto became the Commander-in-Chief of the Combined Fleet, the pro-Germany group formed the mainstream in policy planning in the Navy Ministry.
Shingo Ishikawa, who became the Second Section chief of the Naval Affairs Bureau in November 1940 immediately after the conclusion of the Tripartite Pact, played a central role. Ishikawa enjoyed the deep confidence of Takazumi Oka, chief of the bureau, and had a close friendship with Foreign Minister Matsuoka, who was from the same prefecture, Yamaguchi, as Ishikawa, and former Japanese Ambassador to Italy Toshio Shiratori.
In December, the Navy launched the National Defense Policy Committee, under which each subcommittee was placed—the First Subcommittee dealing with national defense policies, the Second in charge of armaments, the Third for public guidance and the Fourth for intelligence. The committee aimed to work out policies swiftly, and the First Subcommittee took the lead in policy planning. The key members of the First Subcommittee were Ishikawa, Toshitane Takada, chief of the First Section of the Naval Affairs Bureau, and Sadatoshi Tomioka, chief of the First Section of the Naval General Staff.
In April 1941, Prince Fushimi, Chief of Naval General Staff, was replaced by Osami Nagano. Nagano said that officers at section chief level were studying most seriously and it would be better to adopt their opinions. Therefore, Nagano had a strong tendency to accept proposals made by Ishikawa and others. That laid the groundwork for the opinions of the pro-German group members, including Ishikawa, Tomioka, Shigeru Fujii, a staff officer of the Second Section of the Naval Affairs Bureau, and Shigenori Kami, a staff officer of the First Section of the Naval General Staff, to come to the fore in the Navy’s decision-making process.
On June 5, when the negotiations between Japan and the major powers to purchase natural resources, such as oil from the Dutch East Indies, came to a standstill, the First Subcommittee of the National Defense Policy Committee submitted to the Navy leadership a written opinion titled “the position the Navy should take under the current situation.”
The written opinion said that it would be dangerous to make a decision over whether Japan should start a war against the United States only on the basis of the level of materials for military potential. It also said that the First Subcommittee concluded that if Japan could obtain oil in the Dutch East Indies, Japan would be able to cope with the situation with great confidence. Concerning the transportation capacity from the Dutch East Indies, it believed that although Japan would lose about 10 percent of its merchant fleet during a war, it would be possible to compensate for this by building new merchant ships. It urged the Navy leadership to quickly implement plans for the military advance into French Indochina and Thailand.
Chief of the Naval General Staff Nagano accepted the proposals made by the First Subcommittee and strongly asserted the necessity of sending troops to southern French Indochina.
Nagano was a representative plenipotentiary in 1936 when Japan notified its withdrawal from the London Naval Treaty that was set to restrict the number of auxiliary ships. Following Japan’s withdrawal, the naval armament of Japan, Britain and the United States had entered a period without a treaty to regulate their movements and a naval race began.
For Japan, with a limited budget and resources to fight large U.S. fleets that could traverse the Pacific Ocean, it was judged more effective to build extra large battleships with longer artillery range. On the basis of this view, the battleships Yamato and Musashi were built.
Meanwhile, the U.S. Navy also hurriedly pressed ahead with its plan to build warships and the Third Vinson Naval Act and the Stark Act, which provided for a two-ocean navy, were approved in June and July 1940 with a view toward strengthening the U.S. Navy while Germany was engaged in a series of victories over European countries.
At an Imperial Headquarters-Government conference on July 21, 1941, Nagano asserted that there was a chance of victory over the United States, but the chance would diminish as time went by. He added that Japan would be no match for the United States in the latter half of 1942 and if the clash with the United States was unavoidable, the prospects for a Japanese victory would gradually recede.
Nagano believed that Japan would be at the peak of military force compared with that of the United States around April 1941, but that it would fall increasingly behind the United States in a warship-building competition due to the disparity in overall national strength.
The pro-German group in the Imperial Japanese Navy, including Ishikawa, said that they had confidence in a war against the United States if Japan confronted the United States in 1941 and that it was time to start the war. In 1941, Japan still surpassed the United States in naval power in the Pacific Ocean.
On July 31, a day before the United States imposed an oil embargo on Japan, Nagano had an audience with the Emperor and told the Emperor that if Japan lost its oil supplies, its stockpile would last for just two years. He added that if war against the United States started, the oil stockpile would be consumed in 18 months, so there was no choice but to wage war against the United States as early as possible.