He performed his midshipman training on the cruiser Aso, and after commissioning as an ensign, he served as a crewman on the battleship Satsuma.

In 1913, he took time out from the navy to fulfill the obligation of members of his social class to sit for a session in the House of Peers.

After his promotion to lieutenant on 13 December 1915, Komatsu was assigned to the Kongō, destroyers Yūgure and Urakaze and battleship Yamashiro for patrols during World War I.

He subsequently served in a number of staff positions, and traveled to the United Kingdom for further studies in 1925 for over two years at his own expense, during which time he was promoted to commander.

As a vice admiral from 15 November 1940, Komatsu commanded the Ryojun Guard District in 1941, and was commander-in-chief of the 1st China Expeditionary Fleet from 5 July 1941.