Lost records and Japan's Type 6 torpedo

How badly has the loss of Imperial Japanese Navy records affected knowledge of the Type 6 torpedo?

The unfinished torpedo probably advanced only modestly, but the missing records also erase the rationale and evidence behind its development program.

Development began in April 1944, leaving little time before the end of the war. Little practical progress was likely completed during that final year because Japanese industry and research facilities were under severe pressure. The larger historical loss includes the information used to guide development, as well as the results of the tests themselves. Without that rationale, historians cannot reliably reconstruct why particular trials were selected. Archival destruction can erase a development programme's reasoning even when the weapon itself is known to have existed.