Many Goju practitioners in Okinawa are quite irritated by the statement that Yamaguchi is Miyagi's successor. Miyagi spent most of his time teaching in Okinawa and was only in Japan for periods of two to three months at a time. Some doubt if Yamaguchi ever learned all of the Goju system from Miyagi, he may have actually completed the Goju kata at a later date with the help of some senior students of Miyagi. This does not change the fact that Yamaguchi has done more for Goju and karate than any handful of his dissenters combined. For example, he added Taikyoku kata to the Goju system, which are used as training methods for beginners to help prepare for the more advanced kata of the system. Yamaguchi designed and sketched the now famous Goju-ryu fist insignia, modeled after the right fist of Chojun Miyagi.

In 1934 Yamaguchi graduated from Ritsumeikan University, and also completed his development of rules for free fighting. That next year in 1935 he started the All Japan Goju-kai Karate-do Association (in 1955 it became the International Karate-do Goju-kai Association - IKGA), which has increased popularity of Goju in approximately 35 countries throughout the world. This was also the year Yamaguchi began traveling as an intelligence officer for the Japanese Government.

Not too long after Miyagi's first visit, Yamaguchi made his first trek up to Mount Kuruma for austere training. He acquainted himself with a group of Shinto priests, who were involved in spiritual training of their own. As the great masters always do, Yamaguchi learned from the priests and began the harmonization of his Goju training with nature. Some of Yamaguchi's training on Mount Kuruma involved fasting, meditation as well as sanchin stance training under a waterfall in an attempt to unify his body and mind. During this time his strength and mental abilities increased noticeably. Yamaguchi attributed this training to his ability to, "�move without thinking in a natural and mysterious way while practicing."

Back in 1931 Japanese forces, under the guidance and leadership of General Kanji Ishihara seized control of Manchuria. In 1938 General Ishihara asked his friend Gogen Yamaguchi to take a Governmental post in Manchuria, which had been renamed the Republic of Manchu-kuo. During his tour of duty in Manchuria, from 1938-1945, Yamaguchi continued his Goju training. This was fortunate as he had numerous opportunities to apply his training to real life situations. There were two times while in Manchuria, Yamaguchi said he had to exert himself to the fullest of his abilities.

One of those occasions was in 1945 during the Japanese-Russian war. Yamaguchi had received reports that his post was to be attacked by Communist bandits. When the attack began Yamaguchi and some of his men were inside a building making ready to defend themselves. Yamaguchi decided to defend the lower level alone and ordered everyone else upstairs. After he emptied two revolvers into the two dozen or so attackers bearing down on his position, they broke down the door and hand to hand combat ensued. This was actually to Yamaguchi's advantage as the quarters were close and only 5 or 6 men could fit in the room with him. They also had to worry about injuring each other, being alone Yamaguchi had no such restraints. After a time the attackers sounded retreat and withdrew from the town. Gogen Yamaguchi, in hand to hand combat, had fought for his life for 40 minutes straight and only suffered a cut on his left arm, inflicted by a dagger. This event is a true testament to Yamaguchi's quality of training as well as his devotion to that training.

There is another tale of Gogen Yamaguchi's skill from around this timeframe. The story has it that the Russians captured Yamaguchi. Having tried and failed at breaking Yamaguchi by all the normal methods, someone came up with a novel way to just get rid of him. His captors got a tiger and made sure it was hungry. That is when they threw Yamaguchi into the cage with the tiger. The show they got was not one they expected. Instead of being torn apart Yamaguchi kicked the tiger in the nose and smacked it in the head with an elbow. He then leapt on the big cat's back, applied a strangle hold and choked it to death.

There is much debate as to the truth of this story, but at the end of the Japanese-Russian war the Russians took thousands of Japanese in Manchuria prisoner. Yamaguchi was indeed one of those prisoners. He was held for a few months in a POW camp before being sent to a labor camp in Mongolia. The deplorable conditions in Russian labor camps have been well documented, and what Yamaguchi told of his time there confirms this information. The terrible rations, reduction of rations for work not done, interminable roll calls, death by exposure (Prayer at Dawn) and so on. Even through all of this Yamaguchi continued his training and there is a story that says when the Russians found out who he was they had him teach them karate.