Harada was born in the village of Asajawa in Nagano Prefecture on 11 August 1916. After completing school, he joined the Imperial Japanese Navy's naval infantry force in 1933, aged 17. He later transferred to the Navy's aviation branch, and graduated first in the 35th pilot training class in February 1937. Harada was posted to China in October that year during the Second Sino-Japanese War, but was not involved in any aerial combat. While in China he witnessed Japanese military personnel indiscriminately killing Chinese civilians in the mistaken belief that they were soldiers in disguise. In December he took part in the strike on the which led to increased tensions with the United States. Harada was sent back to Japan in January 1938, and subsequently served in several training positions.