Shimada served his midshipman duty aboard the submarine tender Karasaki, and the cruiser Izumi, participating in the Battle of Tsushima during the Russo-Japanese War.

After his commissioning as an ensign on 31 August 1905, he was assigned to the cruisers Niitaka and Otowa, and was promoted to sub-lieutenant on 28 September 1907.

Returning to the Imperial Japanese Navy General Staff as a senior staff officer in June 1932, he served as Chief of the Third Department, Naval Intelligence, where he started espionage operations against the US,[3] and later served concurrently as Chief of the First Department from November 1932 to October 1933 when he assumed total command.

During his term as Navy Minister, he knew of the plans for the attack on Pearl Harbor and approved its implementation.

After a series of major Japanese losses, Emperor Hirohito lost confidence in both the Army and Naval Chiefs of Staff.

Hirohito finally made his displeasure with Shimada known to Tōjō in July 1944, shortly after the fall of Saipan.

After the end of the American occupation of Japan, he was released on parole in 1955 by Prime Minister Ichirō Hatoyama.