He served his midshipman assignment on the cruiser Hashidate, which made along-distance navigational training voyage to Manila, Batavia, Singapore, Bangkok, Hong Kong, Incheon, Busan and Vladivostok in 1901.

During World War I, he was sent to the Netherlands and the United Kingdom as a military attaché to observe modern western warfare firsthand.

On his return to Japan in 1930, he became commander of the Training Fleet, and personally led a training voyage in 1931, going from Keelung to Hong Kong, Singapore, Colombo, Aden, Port Said, Naples, Toulon, Marseilles, Malta, Alexandria, Djibouti, Colombo, Batavia, Manila, Palau and Sasebo.

Sakonji had made a very favorable impression on the Commander in Chief of the Combined Fleet Suzuki Kantarō due to his strong negotiating position during the London Naval Treaty negotiations and subsequent support for the Treaty Faction within the Imperial Japanese Navy.

After the surrender of Japan, most members of the wartime Japanese cabinets were arrested for suspected war crimes by the Allied occupation authorities.