Isoroku Yamamoto was born Isoroku Takano, but changed his name after being adopted by the Yamamoto family. His father was a former low-class samurai warrior. He entered the Naval Academy and graduated in 1904, and participated against Russia. He was seriously injured during the Battle of Tsushima in 1905; he recovered though left with many scars. Yamamoto was nicknamed "80 sen" by some of his favorite geisha girls because he lost two fingers from the said battle (at the time, a geisha manicure cost 100 sen, or 1 yen). He was American educated (Harvard University, 1919-1921);, and became a junior naval attaché to several nations. In 1924, at age 40, he changed his specialty from gunnery to aviation, recognizing the upcoming trend in naval warfare.
During 1926-28, Yamamoto was the senior naval attaché to Washington DC, United States at the rank of captain. After 1928 he returned to Japan, becoming an advocate of air power, and was partly responsible for the establishment of Japanese naval air fleet. He said his farewell to his commissioned carrier, the Akagi, briefly, as a delegate to the London naval disarmament conference of 1930. At the conference he had risen to become a popular figure among the Japanese military elite. He returned to Japan and served as the head of the technical division of the Navy's Aeronautics Department, and then commander of the First Carrier Division, taking the Akagi as his command ship once again. As Vice Admiral, Yamamoto took on the entire Aeronautics Department before becoming the Deputy Navy Minister in 1936. Due to his peaceful nature, his life was seriously threatened by warlike extremists, who at that time influenced Japanese politics greatly during this period of military and territorial expansion. Under the advice of his colleagues, he was transferred to the Combined Fleet as its Commander-in-Chief, escaping feared retribution, or even assassination, against his political views; assassinations could be called commonplace in this period in Japan. Yamamoto was promoted to the rank of full admiral in 1940 at the venerable age of 56. Despite his age, he continue to exercise regularly and keeping in excellent physical shape.