How many merchant ships did Japanese submarines sink?

It appears that Japanese submarines sank a total of “only 171 vessels, including warships, for a total of less than 1,000,000 tons.” (“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.) This is a quote from Kennosuke Toriso.

That was not a particularly effective record. Again, the fault is more the way Japanese fleet commanders assigned their boats, rather than the submarine crews themselves.

Japanese submarines sank only about one ship per submarine. German U-boats sank about 3,000 Allied ships of all types or about three per submarine built. American boats sank about 1,300 enemy ships of all types or about five per submarine.