Shimazaki was a native of Ōita Prefecture and a graduate of the 57th class of the Imperial Japanese Navy Academy in 1929, ranking 31st of 122 cadets. He served his midshipman duty on the cruisers and, after which, as a second lieutenant, transferred to the Imperial Japanese Navy Air Service, enrolling in flight training in 1932. By 1934, he was serving as an instructor at Kasumigaura, Ibaraki in torpedo bomber piloting and techniques. From 1935-1937, he alternated tours of duty as section commander on the aircraft carrier and ground training. With the start of the Second Sino Japanese War in 1937, his group was deployed to the ground base in Shanghai, where he experienced a number of bombing missions as the war between Japan and China escalated. He was transferred to the carrier from March–December 1938, returning to Yokosuka as an instructor. He returned to combat duty on the carrier from November 1939-November 1940, when he was promoted to lieutenant commander. In September 1941, Shimazaki was assigned as equipping officer of the new carrier, responsible for forming its new air wing, with himself becoming its commander when the ship was ready for duty. Shimazaki is best known as the leader of the second wave of the air attack on Pearl Harbor on 7 December 1941. He was piloting a Nakajima B5N2 "Kate" and led the attack group of 54 high-level bombers and 78 dive bombers. For this success he and Mitsuo Fuchida, the leader of the 1st wave of attack, were awarded with an audience with Emperor Shōwa at the Tokyo Imperial Palace on December 25. Four months later, Shimazaki was again on board Zuikaku and participated in the raid on Trinkomalee on 9 April 1942, during which he led 18 "Kates" and bombed the ground facilities of the port city of the British-ruled Ceylon. A month later, Shimazaki participated in the Battle of the Coral Sea. On the morning of 7 May 1942, his attack group took off Zuikaku in search of the US aircraft carriers. They were unable to find the carriers, however, but did locate the fleet oiler and its escort destroyer instead. After further fruitless searching, Shimazaki's colleague from Shokaku, Lt Cdr Kakuichi Takahashi, ordered him to take the torpedo bombers home rather than waste their ordnance on small targets. Shimazaki complied, while Takahashi attacked with his dive bombers, sinking Sims and heavily damaging Neosho. Later that evening, he took part in an attempted night attack on the US carriers. However, the group was jumped by F4Fs before they could find their targets, and nine planes - primarily crewed by division and section leaders - were lost. Shimazaki's group took particularly heavy losses - five planes lost out of nine - but he survived to return to Zuikaku. The following day - 8 May 1942 - Shimazaki led Zuikaku's "Kates" in the attack on. Teaming up with his Shokaku counterparts, they succeeded in crippling the carrier, which later sank. However, his plane took heavy damage, forcing him to ditch on his return.
