Early life and career
During World War I he served as commander of a torpedo boat. For his bravery in a combat action he received a decoration at war's end in November 1918. From 1923 to 1928 he served in China as naval attache to the Italian embassy. In 1928 he assumed command of a destroyer, and then a cruiser in the early 1930s. During the Spanish Civil War he was the commander of two groups of light ships. He also participated in the Italian occupation of Albania in April 1939.
World War II
With the rank of Ammiraglio di Squadra, Iachino participated the Battle of Cape Spartivento in 1940 as commander of a cruiser squadron and, on 9 December 1940, he replaced Admiral Inigo Campioni as commander of the main battle force of the Regia Marina. His actions in the Battle of Cape Matapan (March 1941), during which three Italian heavy cruisers and two destroyers were lost, have been the subject of much criticism since then; despite this, Iachino wasn't relieved of command, and he subsequently led the Regia Marina in the First Battle of Sirte (December 1941), Second Battle of Sirte (March 1942), and during Operation Vigorous (June 1942). On 5 April 1943 he was replaced by Admiral Carlo Bergamini.
He retired in 1954 with the rank of Ammiraglio d'armata (Admiral), and died in Rome in 1976, at the age of 87.