It was just hours before Japan’s surprise attack on Pearl Harbor on Dec. 7, 1941. In Tokyo, Prime Minister Gen. Hideki Tojo was “perfectly relieved” and “tipsy,” convinced Japan would win any conflict with the United States after having finished all the administrative procedures to wage war against American and British forces in Hawaii and Asia.

In a meeting with two influential bureaucrats — Internal Affairs Vice Minister Michio Yuzawa and Army Vice Minister Heitaro Kimura — at the Prime Minister’s Office at 8:30 p.m. on Dec. 7, Tojo told them that Emperor Hirohito (posthumously known as Emperor Showa) was “not wavering” and showed no signs of “lingering regret” about the government’s decision to end diplomatic talks with the U.S. and Britain to avoid war.

The revelations were uncovered in a five-page memo Yuzawa wrote that night that was discovered by Takeo Hatano, the owner of a secondhand bookstore in Tokyo. The memo’s contents were first reported by the Yomiuri Shimbun on Monday. The Japan Times confirmed the text later in the day.

“I’m perfectly relieved. You can say we have already won (the war), given the current situation,” Tojo was quoted as saying in the memo, apparently referring to Hirohito’s endorsement of his war preparations.

“This was a private chat. I think Tojo was saying what he was actually feeling,” said Takahisa Furukawa, a professor of history at Nihon University and one of two historians The Japan Times interviewed by telephone.

Furukawa and another historian who examined the paper said the memo was exceptional in that it for the first time showed Tojo’s behavior just hours before the attack that triggered America’s entry into World War II.

It also revealed that Emperor Hirohito — who had previously been very much concerned about any possible conflict with the U.S. — remained calm after effectively endorsing the government’s decision to wage war on the U.S. several days before Pearl Harbor, Furukawa said.

Tojo, who was appointed prime minister because of his passionate admiration for and loyalty to Emperor Hirohito, has been widely described as having the personality of a bureaucrat rather than a decisive military leader.

The memo, which quoted Tojo as saying that he was “perfectly relieved” after finishing the administrative procedures for launching the war and receiving the Emperor’s approval, appeared to lend credence to this view, Furukawa said.

At the same time, Tojo appeared overly optimistic in his conviction that Japan would prevail even before the Pacific War had begun. The memo showed he was “very narrow-sighted,” said University of Shizuoka history professor Atsushi Moriyama, because Japan’s fate would ultimately be determined by a number of other factors — not merely the war preparations or an Imperial endorsement.

“The memo vividly showed (Tojo) was very happy because the Emperor approved of his preparations,” Moriyama said. “This (memo) is invaluable” to understanding him and the situation in Japan in the days before the war.

Moriyama pointed out that before the decision to go to war, top government and military leaders had maintained that Japan might be able to win some of the initial battles but doubted whether it could maintain this momentum for three years, given its limited resources, including oil.

The memo suggested Tojo had dismissed such critical logistical issues once the Emperor endorsed the decision, he said.

Ultimately, while the Pearl Harbor attack proved a success, Japan was eventually overwhelmed by the military might of the U.S., which was backed by its massive manufacturing capacity. Japan surrendered in August 1945 after most of its major cities were devastated by U.S. air raids and two atomic bombings.

Yuzawa’s memo was dated 11:20 p.m. on Dec. 7, 1941, a few hours after the meeting with Tojo and shortly before the Pearl Harbor attack.

He wrote that he recorded the day’s events because he “was deeply moved and felt honored” as he engaged in war preparations that he said would “determine the fate of the imperial state.”

In the memo, Yuzawa quoted Tojo as saying: “If His Majesty feels any lingering regrets about the negotiations with Britain and the U.S., some of his expressions would look somewhat melancholic. But this can not be seen anywhere, which is a result of his determination.”

Tojo was also quoted as saying that the entire military had prepared for the war under strict orders, based on the Emperor’s determination.