How were Japanese submarines lost?

Most, perhaps about 80, appear to have been lost to our Anti-Submarine Warfare (ASW) forces. However, the exact numbers are difficult to determine. Our ASW forces included destroyers, destroyer escorts, aircraft and even a PT boat. The USS England (DE-635) sank five in just 7 days, and a sixth a few days later, all just before the Battle of the Philippine Sea. The Allied ASW forces of Britain, Australia, New Zealand and India sank about eight more.

U. S. submarines sank 18 Japanese boats, and British submarines sank two more. The Japanese submarines were on the surface when they were sunk. In WW2, U. S. submarines did not have the capability to safely attack hostile, submerged boats.

There were also about 22 losses to mines, collisions, accidents and unknown causes. (“Imperial Japanese Navy Submarines 1941-45” by Mark Stille, page 45.)