Did the Japanese ever change the focus of their submarine force?

Apparently not. “Japanese submarine doctrine clearly focused on the enemy’s battle fleet at the expense of developing the strategy and tactics required to attack the enemy’s commerce and sea lines of communication.” Mr. Stille adds: “All considered, the exploits of the [Japanese] Imperial Navy’s submarine force were among the more disappointing stories of the Pacific War.” (“Imperial Japanese Navy Submarines 1941-45” by Mark Stille, page 6.)

“Throughout the war, destruction of commerce was undertaken only when the fighting strength of the fleet allowed.” (“Sunk; The Story of the Japanese Submarine Fleet 1941-1945” by Mochitsura Hashimoto, page 62.)

“But the Japanese submarines never made a serious attempt to attack American merchant shipping in the Pacific, and none at all to disrupt the traffic through the Panama Canal …. The Japanese admirals stuck rigidly to the view that submarines were first and foremost an adjunct to the battle fleet, even when they were forced to use the boats to move soldiers and supplies unobserved during the Pacific Campaign.” (“The Pacific Campaign, the U.S.-Japanese Naval War 1941-45” by Dan van der Vat, pages 119-120.)

Kennosuke Toriso, Operations Officer on the Sixth Fleet (submarines) staff stated: “From the outbreak of the war, the Japanese Navy had stuck to its long-cherished ‘one-big-battle’ in which all naval arms - surface, air and underwater – were to be used once and for all. The employment of the underwater arm was not excepted, even after the loss of Guadalcanal turned the tide against us.”  (“The Japanese Navy in World War II: In the Words of Former Japanese Naval Officers”, by David C. Evans, ed. and trans., Naval Institute Press, 1986 page 440.)

Yet, when the larger battles of the Philippine Sea and, particularly Leyte Gulf, which were the closest things to the big battle the Japanese sought, their submarines were practically non-participants.