Hara attended the Naval Staff College in 1923-24 and then was promoted to lieutenant commander. In December 1926, Hara was assigned to his first command, that of the destroyer . He was promoted to the rank of commander in 1929, and then he served as an instructor at several of the naval ordnance schools during the early 1930s. Hara was given command of the gunboat in 1932, and he was promoted to captain in 1933. During 1933–34, Hara was assigned as the naval attaché at the Japanese Embassy in Washington, D.C.. When he returned to Japan, Hara took command of the cruiser from November 1934 to November 1935, and next he held a number of staff positions in the Imperial Japanese Navy until he was promoted to rear admiral on November 15, 1939.