There he became close friends with his classmate Isoroku Yamamoto, who would become a prominent admiral of the Imperial Japanese Navy during World War II.

During the Russo-Japanese war, Hori served in Tōgō Heihachirō's flagship Mikasa, and participated in the Battle of Tsushima.

[1] During the Washington Naval Treaty negotiations in 1922, he served as an attendant to Prime Minister Katō Tomosaburō, himself a former admiral.

Hori and other admirals of the Treaty Faction believed that the limitations would serve Japan's interest in the long run and prevent a costly war with the western powers.

In 1934, militarists of the Fleet Faction headed by Prince Fushimi Hiroyasu and Sankichi Takahashi, gained supremacy over Navy Minister Mineo Ōsumi.

That same year Hori and other Treaty Faction opposition leaders were silenced or forced to retire in the Ōsumi purge.

As the right-wing and militaristic hardliners cemented their influence in the Navy, Yamamoto considered retiring, however, Hori convinced him to stay.

An extensive and revealing collection of letters written by Yamamoto to Hori, before and throughout World War II, is stored in the Oita Prefecture Ancient Sages Historical Archives.

[1] In 1951, Hori was part of an advisory committee composed of former Imperial Japanese Navy officers to oversee the formation of the Japan Maritime Self-Defence Force.