Greetings. We have here a late WWII Seikosha Imperial Navy pilot's chronograph. Most likely made in 1944/1945. Pilots chronographs had extra heavy bows, held on with screws, which were much more robust than the bows of other military pocket watches and chronographs produced by Seikosha during WWII.

Those with an interest in collecting WWII Japanese weapons are well aware of the decline in the quality of Japanese military rifles and pistols in the last years of the war. There was a lot of cost cutting to maintain production. As we will see, this was also true for military timepieces.

This late war chronograph has less information engraved into the back of the case. There is no serial number, only that it is a type of timer or stop-watch.

Compare the above with a back of pilot's chronograph from a few years earlier. The character within a circle stands for the word, air, which indicates that the timepiece was intended for issue to an aircraft pilot. The serial number is stamped using Japanese numerals.

Inside the outer back cover there are Japanese Imperial Navy inspection stamps.

All of the other WWII era Japanese chronographsI have seen have had double hinged back covers. As a cost/production savings, the inner cover of this late war watch does not have a hinge.

The back of the dial also has various Navy inspection stamps. These were applied with ink.

Early WWII chronographs were issued with 17 jewel movements like this one.

The WWII Seikosha chronographs were manufactured with some high quality features. One of which is this sweep second wheel brake (see pointer). While timing something, after the stop button is pressed, this brake will hold the sweep second hand in position, so that it can't be moved if the watch is bumped or jarred. Many other chronographs lack this feature, relying instead upon a drag spring under the sweep wheel to hold it in position. It would appear that all of the WWII Seikosha chronographs kept the brake system, even the very late war examples. Such as this one.
Note; This image is of the late war movement. It has only 7 jewels to cut down on production expenses. One of the jewels, the balance jewel in the pillar plate was cracked, so I had to replace it in the course of cleaning and overhauling the movement. The balance pivots needed polishing and the hairspring was slighting bent.
As I worked on this movement, I could tell from various scratches, etc that I was not the first person to work on it. I could almost hear the echo of the past watchmaker's obscenities as he delt with all of the extra little screws and uncooperative little chronograph springs!

There were several other little changes to this late war movement. I noticed that some of the chronograph springs had only one steady pin instead of two, as you can see in the picture.

In general, it appears that Seikosha did a very good job with the manufacture of this timepiece during a time of national crisis. Fortunately, Seiko had moved there factory out of Tokyo before the war, which saved their factory from destruction.

After a considerable amount of work, the late war Seikosha pilots chronograph is now keeping time much better than expected.

There were several variations of these timepieces, with different markings for issue to submarine/torpedo boats, navigation, artillery, and so forth. But the pilots had the distinctive heavy duty bow.

Gregg, vary interesting. Enjoyed your information about this watch.

Curly

I forgot to mention, that as part of the overhaul process a new mainspring was installed. Chronograph mainsprings are stronger (thicker) than regular watch mainsprings to power the extra timing, or stop-watch mechanism.