Mutsu Heihachiro was born in 1895 in the family holdings outside of Kobe, Japan.  He is the grand-nephew of Admiral Togo Heihachiro, hero of the great battle in Tsushima Straits in the Russo-Japanese War.  His grandfather, who also served in the Japanese Navy,  was killed in an explosion of a Japanese gunboat during the Sino-Japanese War.  As a youth he received training in the samurai tradition.  He is an excellent swordsman and skilled in the use of pistol and rifle.

In 1912 he entered the Japanese Navy as a cadet and was soon promoted to Lieutenant.  In 1914 he served aboard the armored cruiser Idzumo in support of the siege of the German colony of Tsingtau (Shantung Peninsula, China).  The disorder and confusion reigning in China at this time convinced him that it was necessary for Japan and the West to intervene and restore order.

In 1917 he served aboard the destroyer Sakaki in support of Entente naval activity in the Mediterranean.  Based in Malta, he participated in the escort of several troopship convoys until his ship was torpedoed by an Austro-Hungarian submarine off the coast of Crete in June.  After several months in hospital in Alexandria, he returned to Japan and was promoted to Lieutenant Commander.

After the conclusion of the Armistice in November 1918, Mutsu travelled to Paris as part of the Japanese delegation to the peace conference at Versailles.  He was deeply disillusioned by the greed and arrogance of the Western colonial powers.

In 1920 he was stationed at the Japanese Embassy in Washington, D.C., as assistant naval attache.  He used this opportunity to polish his English language skills and met many influential Americans.  He also made several visits to the U.S. Naval Academy at Annapolis.  Mutsu was impressed with what he saw of the United States, particularly its vitality and energy.

After returning to Japan in 1922, Mutsu served aboard the cruiser Akashi until his retirement in 1924.  He was then hired as a Supervisor at a Japanese warehouse in Shanghai (Fujian Export and Import).