WWII Japanese sextant

This sextant was given to me by my grandfather before he passed away. He was stationed in Japan right after the surrender. The told me that while he was stationed in Japan, he had worked on converting a Japanese Aircraft Carrier into a Repatriation ship (a troop transport used for bringing Japanese troops back home). He told me that he had taken the sextant from the bridge of that ship. Now the question is...

Which ship is it from?

I know it was an aircraft carrier. My research shows that only three carriers were used for repat. duty after the war: Hosho, Katsuragi and Kumano-Maru. I believe that it was NOT from the Hosho since the Hosho was comissioned in 1922 and operated throughout the war. That being the case, her instruments would have been much more used than this one. This sextant was issued July 9, 1944. A bit late for the Hosho. The Katsuragi was launched January 19, 1944 and commissioned October 15, 1944, so the date works well with that timeline. The Kumano-Maru was launched January 28, 1945 and commissioned March 31, 1945. A little late to have been outfitted with this unit. But I would like something a bit more tangible, proof wise.

I have learned that the Kumano-Maru was an Army ship. That may make a difference. I am currently trying to determine if the Army ships were issued the same instruments and, more importantly, if the 'proof' markings were the same as the Navy. This sextant, and the documentation that goes with it, has little anchor proof marks (see here and here). Now, if the Army ships used different markings, I can eliminate the Kumano-Maru and I have my answer! If anybody knows for sure, please email me!

Overall shot of the box.

Side of the box with handwritten script. Does anyone know what this says? If you do, please email me!

ID plate on the outside of the box.

Overall shot of sextant in the box.

Better view of unit in box.

Issue certificate with corrections.

Detail of the certificate stamps.

Overall view from the optic side.

Overall view from the handle side.

This shows the battery compartment in the handle.

Detail of the knob and rail.

Close-up of the optic.

Marking on the rail.

Stamps on the sextant.

Mirror plate. Due to the finish, I suspect this is the original piece. My guess is the one currently on the unit is a newer (but compatible) part purchased later by my grandfather from Tamaya. (see letter below)

Spot in the case for extra bulbs.

Space for viewfinder filter.

The included screwdriver goes here.

Latchable compartment to store extra batteries. This thing has it all!!

Detail of the side latches on the case. Very nicely done.

The letter sent by Tamaya regarding replacement parts for the sextant. Dated 1973. Pretty cool!

Blueprints of the MS-3 Sextant, sent by Tamaya to my grandfather so he could figure out what extra parts he could use from the current production model.