Relying on the special relationship of the Yamamoto family, Yamamoto probably knew the news that the Japanese army was about to open up a battlefield in the south, so he took advantage of the fact that the troops stationed in northern Jiangxi had not been transferred, and carried out two large-scale encirclement and suppression operations against Xiao Xiong's anti-enemy special forces in northern Jiangxi, in a vain attempt to wipe out the anti-Japanese armed forces in the Jiujiang area under his jurisdiction in one fell swoop.

The Ninth Theater Commander's Headquarters reported to the Central Military Commission the summary of the Second Battle of Changsha, especially the intelligence analysis of the Jiangxi Northern Einsatzgruppen. The higher authorities immediately handed over the report to the Technical Research Office of the Kuomintang Military Commission in Chongqing, a mysterious intelligence department known as the "Chinese Black Room" that specialized in listening and deciphering enemy codes.

Speaking of "China's black room", we have to start with the American Herbert Yadley.

Herbert Yadre was a confidential officer in the U.S. State Department, and after the outbreak of World War I, Adrey created a classified code-breaking unit within the State Department, codenamed "The Black Room", and he is known as the "Father of American Cryptography." He was famous for repeatedly cracking enemy telegraphs in World War I, and Herbert Yardley is known as the father of American ciphers.

In 1938, after Dai Li learned about Yadley's situation from the telecommunications expert Wei Daming, he secretly contacted Hu Shih, the Chinese ambassador to the United States, and hired Yadre to China to help crack the Japanese military code on the condition of an annual salary of 10,000 US dollars. In November of that year, Yardley, who assumed the pseudonym "Robert Osborne", arrived in Chongqing via Hong Kong.

After the start of the Anti-Japanese War, in order to strengthen the ability to decipher, the military commander established the Telecommunications Technology Research Institute in 1939 in a large house at No. 94 Shenxiandong Street in Chongqing, secretly codenamed "Huolu", directly under the leadership of the Supreme Military Council, and secretly hired Herbert Yadley through the Chinese military attache in the United States.

Dai Li mobilized more than 50 staff, more than 50 listening machines, and more than 200 listeners to focus on the Japanese Army's cryptographic system. During his two years of working in China, the "Huolu" intercepted more than 220,000 cipher telegrams from the Japanese Army, focusing on more than 20,000 copies, and achieved considerable results.

At that time, the Japanese naval air force often sent planes from Hankou to bomb Chongqing, and the secret telegram group under the Kuomintang Military Command Bureau repeatedly intercepted the coded telegrams sent by Japanese spies lurking in Chongqing.

Beginning in March 1939, the Yadre group intercepted a large number of telegrams written by the Japanese in new, more complex and difficult codes, and before they could report this information upwards, on May 3 and 4, Japanese planes flew directly from Hankou to Chongqing for two consecutive days, dropping hundreds of bombs. The next day, more than 20 Japanese planes attacked Chongqing again. One phenomenon caught Yadre's attention: Why didn't the air defense units deployed by the Kuomintang in the urban area of Chongqing shoot down a few enemy planes? Through the introduction of his Chinese girlfriend Xu Zhen, Yadre became acquainted with a battalion commander of a Kuomintang anti-aircraft artillery regiment stationed in Chongqing, who was nicknamed the "one-armed thief".

After following it closely, Yardley discovered that the new secret messages sent by the Japanese spies were beginning to be mixed with some English letters. Adrey speculated that the Japanese spies had used the method of compiling the "book code", which was based on an English-language novel. At this time, the Kuomintang Military Command Bureau provided an important clue: the "one-armed thief" sometimes openly used the radio station of a nearby Sichuan infantry division to exchange secret messages with his "friends" in Shanghai, and he was most likely a traitor. Yadre set his sights on the "one-armed thief".

Yadre and Xu Zhen went to visit the house of the "one-armed thief". Xu Zhen found a novel "The Earth" by the famous American female writer Pearl Race in the study of the "one-armed thief", and the first word on pages 17, 18, and 19 of the book was drawn with a pen. The "one-armed thief" was the eyes and ears of Wang's puppet government in Chongqing, and he formed a spy network with the German adviser Her Weiner and others in the Nationalist government, and secretly told the Japanese bombers to maintain a flight altitude of 3,660 meters to avoid the fire of the Kuomintang anti-aircraft guns with a range of only 3,050 meters. Subsequently, the "one-armed thief" and other moles were arrested and shot.

In July 1940, Yadre returned to the United States. The pamphlets he left behind that specialized in cryptography techniques such as "translocation" and "substitution" have helped China a lot.

In order to integrate the technical force of code breaking against Japan, in 1940, the Supreme Military Commission explicitly ordered the establishment of the Technical Research Office of the Kuomintang Military Commission. And imitate the name of Yardley's "American Black Room" back then, and call it the "Chinese Black Room".

The military technology room has about 400 to 500 people, and there are six groups under it, and each group is divided into the following groups: The first, second, and third groups are responsible for deciphering Japanese cipher codes, the fourth group is responsible for receiving reports, the fifth group is responsible for general affairs, and the sixth group is responsible for deciphering Chinese cipher codes. Of these, four groups have the largest number of personnel. The military technology room is located in the Liujia Garden on the south bank. In order to facilitate the investigation, the fourth group was set up on the high hill opposite Liujia Garden, that is, Rentou Mountain. At that time, the cipher code intercepted by the listening team was mainly sent to Liu's garden on horseback to be deciphered.

In the deserted Huangjuya Rentou Mountain in Nanshan Town, a southern suburb of Chongqing, the sign of "Central Industrial Experimental Research Institute" is hung at the door of a simple building, where the administrative and deciphering organs of the black room are secretly set up. On the opposite side, two kilometers away, the summit of Rentou Mountain is its password listening office.

There are armed soldiers patrolling a kilometer from Rentou Mountain, and even local villagers are forbidden to enter.

The materials and personnel inside are all through horses, and on the slope of the hillside on the east side of Rentou Mountain, there is a horse farm. There is a house in front of the racecourse, which is the entrance hall for reception, and there is also a diesel engine that generates electricity at the door. There are many large trees on the South Mountain, and it is common to see Japanese planes flying around the mountain, but the Japanese do not find the houses or people or animals below.

There are no people living within a few hundred meters of Rentou Mountain, and if there is no one to guide you, you will not be able to find this remote and hidden place.

On the mouth of Rentou Mountain, on an open area of nearly 1,000 square meters, there are several rows of houses. Next to the house, there is a basketball court. Go up 50 meters, to the peak of Rentou Mountain, there are more than a dozen irregular holes around the peak, there are half-human tall wild grass outside the cave entrance, it is difficult to find without walking to the edge of the cave. The mountain peak is almost hollowed out, and the tunnels crisscross it, about two meters high, with different widths and unevenness.

There are many radio stations in the tunnels of Rentou Mountain, which can receive and receive telegrams, and can detect in advance when Japanese planes will come to bomb Chongqing.

Any cipher code deciphering agency, listening and deciphering are definitely divided into two places, especially Huang Jueya Rentou Mountain. The entire mountain peak is hollowed out, and several U-shaped tunnels are relatively independent, and in order to achieve mutual secrecy, each tunnel is a department, each with a different task.

The report of the Ninth Theater Commander's Department soon reached the hands of Chi Buzhou, the chief commissioner of the Kuomintang "Technical Committee of the Military Commission".

Chi Buzhou, born in Minqing County, Fujian Province, went to Japan in 1930 to study at the University of Tokyo, graduated four years later, served in the Military Attache Office of the Chinese Embassy in Japan, and married a Japanese girl, Eiko Shirahama.

On July 25, 1937, Chi Buzhou returned to China with his wife and three children, and soon after joined the Second Confidential Unit of the General Affairs Group of the Central Survey and Statistics Bureau of the Kuomintang.

On April 1, 1940, Chi Buzhou entered the Technical Research Office of the Kuomintang Military Commission.

After Chi Buzhou received the telegram from the Ninth War Zone, he felt that this telegram was very important. He immediately organized personnel to analyze a large number of Japanese military telegrams intercepted in the recent period.

In recent times, the Black Room has made great achievements in cracking the Japanese telegraph.

One day in May 1941, the Nationalist Government sent this extremely important information that "Nazi Germany decided to start attacking the Soviet Union within about one week around June 20" to Zhou Enlai through Mr. Yu Youren, and Yan'an quickly handed over this important information to the intelligence officers of the Soviet Red Army.

In the early morning of June 21, 1941, the Soviets received the news from a German deserter that the German army was about to attack, so that the Soviet army knew the news 24 hours before the start of the war, thus avoiding the catastrophe. And this important information was intercepted and broken by the Black Room.

In May 1941, Chi Buzhou found that the number of telegrams between the Japanese Ministry of Foreign Affairs and the Japanese Consulate General in Honolulu suddenly increased dramatically in the deciphered Japanese diplomatic secret telegrams, and the content of the telegrams was always that the Ministry of Foreign Affairs asked the Japanese Consulate General in Honolulu to report: the number and names of US warships in Pearl Harbor; the location of the mooring; the time of entry and exit; the timing and pattern of the rest of the U.S. military at Pearl Harbor; Hawaii climate conditions, etc. The Black Room promptly reported this anomalous information to his superiors. Later, the Nationalist Government transmitted the information to the U.S. government.

One day in mid-November, not long after Chi Buzhou received the report from the Ninth Theater, the "Military Technology Office" deciphered a secret Japanese diplomatic cable, which read: The Japanese Government is preparing to send its former ambassador to Germany to the United States to carry out the task of "peace talks" in an attempt to form an alliance with the United States. They hastened to report the deciphered telegram to the highest authorities.

The Chinese authorities immediately called US President Roosevelt and demanded that the United States declare war on Japan, otherwise China would "sell itself out." The U.S. government attaches great importance to this, and after consulting with China, Britain, Australia, and other countries, it handed over a memorandum to the Japanese government. The main conditions set forth in the memorandum were: the demand that Japan withdraw all its troops from China and Indochina; In China, no government or regime other than Chiang Kai-shek's government may be supported; and the abrogation of the alliance treaty between Japan, Germany, and Italy. Obviously, these conditions in the memorandum could not be accepted by the Japanese Government, and for this reason the "peace talks" between the United States and Japan ultimately did not lead to anything.

After that, Chi Buzhou organized a "military technology room" to decipher a "Japanese diplomatic secret telegram" and found that the Japanese government was holding commercial negotiations with the Soviet government, and the subject of the negotiations was Japan's preparation to exchange rubber for Soviet timber. Japan is already a resource-poor country, where do rubber resources come from?

Based on the above information, combined with the large-scale attack of the Japanese army on Changsha and a series of military operations such as Yamamoto's two frantic attacks on the Ganbei Special Forces, Chi Buzhou deduced that the reason why the Japanese army wanted to take action was that it would soon go south to invade and occupy the countries of Southeast Asia rich in rubber.

Therefore, he urgently drafted a report and handed it to the highest authorities, the report that the Japanese army was about to move south, preparing to launch a war of aggression against Southeast Asia.