Shimazu returned to specialized weaponry schools and became a torpedo and naval artillery expert. As a sub-lieutenant, he served on the battleship and again on Katori. From 1911-1913, he left active service to assume his seat in the House of Peers, returning in December 1914 to the battleship after having completed navigation and advanced gunnery training. As lieutenant, he served aboard the and during World War I, but saw no combat.
