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 Iwate and Haguro, after which, as a second lieutenant, transferred to the Imperial Japanese Navy Air Service, enrolling in flight training in 1932.

[4] In September 1941, Shimazaki was assigned as equipping officer of the new carrier Zuikaku, responsible for forming its new air wing, with himself becoming its commander when the ship was ready for duty.

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.

[6] 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.

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.