During this period, Ueshiba was invited to teach at a number of military institutes, due to his close personal relationships with key figures in the military (among them Sadao Araki, the Japanese Minister of War). He accepted an invitation from Admiral Sankichi Takahashi to be the martial arts instructor at the Imperial Japanese Naval Academy, and also taught at the Nakano Spy School, although aikido was later judged to be too technical for the students there and karate was adopted instead. He also became a visiting instructor at the Imperial Japanese Army Academy after being challenged by (and defeating) General Makoto Miura, another student of Takeda Sōkaku's Daitō-ryū. Takeda himself met Ueshiba for the last time around 1935, while Ueshiba was teaching at the Osaka headquarters of the "Asahi Shimbun" newspaper. Frustrated by the appearance of his teacher, who was openly critical of Ueshiba's martial arts and who appeared intent on taking over the classes there, Ueshiba left Osaka during the night, bowing to the residence in which Takeda was staying and thereafter avoiding all contact with him. Between 1940 and 1942 he made several visits to Manchukuo (Japanese occupied Manchuria) where he was the principal martial arts instructor at Kenkoku University. Whilst in Manchuria, he met and defeated the sumo wrestler Tenryū Saburō during a demonstration.