Sino-American Spy Activities
The Tokeitai (特警隊, Tokkeitai?, Naval Secret Police) was the Imperial Japanese Navy's police equivalent to the Imperial Japanese Army's Kempeitai military police service.
The original Tokeitai was known as the General Affairs Section and concerned itself with police and personnel work within the Navy: personnel, discipline and records. It took a more active role, partly to keep the Kempeitai and Army from meddling in Navy affairs. Smaller and more low-key than its rival, it was no less brutal. It was especially active in the areas of the South Pacific, the Naval Control Area, as well as maintaining a presence as pervasive as the Kempeitai had. It had the same 'commissar' roles, in relation to exterior enemies or suspicious persons, and watching inside units for possible defectors or traitors, under the security doctrine of "Kikosaku".
Attached to Navy units, they served as Colonial police in some occupied Pacific areas. Later accusations of war crimes were made against them in that role such as the coercion of women from Indonesia, Indochina and China into sexual slavery. 
Additionally to mentioned police service, Tokeitai was the operative branch of Naval Secret Services of Japanese Navy, for recover and analyzed information and making undercover operations. Its members also provided local security in near naval bases. In the final weeks of the Pacific War, they were amongst the security units prepared for combat against invasion of Japan.
An Imperial Navy Lieutenant Commander and subversive agent, a former exchange student at California's Stanford University, had recruited an American spy, former Navy yeoman. Starting with a $500 lure and $200 monthly payment, Japanese agents persuaded the American to board U.S. Navy ships dressed in a yeoman's uniform, to obtain intelligence from the crews. The Japanese recruited an American in San Pedro, two hours drive up the California coast, and also the location of U.S. shipping and naval units. This American was detected by the U.S. Office of Naval Intelligence (ONI) and was later sentenced to 15 years in prison.
The Japanese, like their counterparts in China, developed espionage programs by linking secret societies with ultranationalist aims such as Genyosha (Dark Ocean Society), Kokuryu-ku (Amur River Society, the Black Dragons link) and organized criminal enterprises such as Yakuza crime syndicates. Indeed, Dark Ocean and the Black Dragons supplied espionage and subversion services to the Empire in Korea in 1895 and perhaps earlier. Dark Ocean founder and Black Dragon mentor Mitsuru Toyama, as well secret society links to the Japanese Kempei Tai, a functional equivalent to Hitler's Gestapo that relied upon the secret societies for manpower and support.
The Black Dragons were the Amur River Society (Kokuryu-kai) in 1930s and 1940s Japan. The Black Dragons were ultra-nationalists heavily involved in the conquest of China, and as spies and fifth columnists subverting nations targeted for conquest. The Black Dragons were active up and down the Pacific Coast of North and South America.
Black Dragons were a concern to Lieutenant Commander K. D. Ringle of U.S. Navy Intelligence and other security officials. They were a secret society with political aims. Many of its members served in industry and government including diplomatic posts and bureaucratic and military roles such as the Kempei Tai secret political police. The veiled relationship of secret societies such as Black Dragon to government and business exemplifies a Japanese social phenomena.
Secret Japanese documents titled "The Three Power Alliance and the American/Japanese War" were alleged to have been stolen from an intelligence officer of the Black Dragon Society by an anti-Japanese Korean patriot. The documents were purported to detail Japanese war plans for the simultaneous invasion of the Panama Canal Zone, Alaska, California and Washington State. He was said to have obtained the documents by clandestine means in a Los Angeles hotel room in 1940.
In the Dutch East Indies and the Philippines, as in the U.S. and Mexican west coasts, throngs of Japanese fishermen pulled nets and took notes and pictures for the Empire. Japan's fishing fleets were augmented by farmers, mining engineers, industrialists and merchants, barbers, house-boys, maids and prostitutes, especially in those areas designated as part of Japan's Greater East Asia Co-Prosperity Sphere. In this sea of ordinary Japanese was submerged a potent fifth column of spies, subversives and saboteurs. There is a story of a French writer traveling worldwide, observing Japanese spy rings operating in Malaya, India, Burma, Ceylon, Thailand and as far away as Middle East, Morocco, Port Said, Egypt and Italian-occupied Ethiopia.
In the period from about 1895 to 1941, Japan encouraged emigration of its citizens to nations bordering the Pacific Ocean, including the United States. These Japanese were often referred to as doho, or "compatriots". The position taken by Tokyo was that the doho held dual citizenship, with loyalty to Japan, and loyalty to the Emperor first and foremost. While unknown numbers of Japanese citizens rejected the demands of being doho, many did not. The doho created security problems for Asian nations, the Pacific islands and for the United States and Canada. Routinely denied by Japanese-Americans, doho performed espionage and subversive duties for Japan on U.S. soil. Japanese men returned to Japan to serve the Tenno. Thousands of Japanese-American men renounced their loyalty to the U.S. and demanded repatriation to Japan during World War II. Black Dragons disrupted U.S. internment camps. Declassification of U.S. security files including top secret intercepts of Japanese Code Machine and other ciphers has confirmed and added to the body of information on doho.
There were among the Japanese both alien and United States citizens certain individuals, either deliberately placed by the Japanese government or actuated by a fanatical loyalty to that country, who acted as saboteurs or agents. This number is estimated to be less than three percent of the total, or about 3500 in the entire United States.
The most dangerous of these people were either in custodial detention or members of such organizations as the Black Dragon Society, the Kaigun Kyokai (Navy League), or the Hoirusha Kai (Military Service Man's League), or affiliated groups. The membership of these groups was already fairly well known to the Naval Intelligence Service or the FBI and could be immediately placed in custodial detention, irrespective of whether they were alien or citizen. Another example, in the Southeast Asia area, were Japanese living in Malaya before World War II carrying out subversion and providing intelligence information, troops and war materiel. These Japanese immigrants, or first generation descendants of Japanese born in Malaya, were considered doho, or compatriots by Japanese traditions and law. Their allegiance to the Emperor and Japan was assumed by Japan's leaders. The doho in Malaya included the Japanese Editor of a local journal, a Japanese diplomat (arrested for espionage), thousands of Japanese prostitutes, businessmen, dentists, photographers and barbers.
The policy of this editor was to oppose the pro-England, pro-Southeast Asia policies of local newspapers and soften public opinion in Japan's favor. The prostitutes, passed on pillow talk, and the businessmen, dentists, photographers and barbers were all well-placed to collect intelligence, take photos and glean intelligence while hearing the chatter of their customers and social contacts.