[Admiral Von Gerlach]

In many ways the IJN submarines were indeed strong and superior ..and much effort was put into creating a large and versatile force. But the submarine force suffered from two major problems: one was mechanical and one was strategic. Many of the power plants were somewhat old fashioned and problematic. Some of the large boats had a major problem in surfacing and submerging. Changes between Desiel and electric required a mechanical change in drive chain that severly limited the speed of these essential manuvers for a subsurface craft.

And the major problem was Fleet command saw and continued to see to the very end of the war the submarine force's main task as being support of the surface fleet. they never set up a strong and aggresive campaign against merchant shipping or really used the qualities of the fine boats that the IJN had including the 17 seaplane carriers in the sub force.

Sad for them but lucky for the allies.