- In the first year of the war, the Russian generals strongly blamed their defeats on the lack of sufficient heavy artillery. So maybe Japan let itself be talked round to support its old foe. After all, Japan did fight on the allied side.
- A Russian booty of the Russian-Japanese war (seems unlikely, and too easy anyway)?
- A Japanese gun from Liaodong, handed over to Russia after the Japanese-Chinese war (seems unlikely too)?
I also remeber that the Japanese navy had some presence in the Mediterranean (one destroyer was torpedoed by a German submarine) but I dont have any more info about this. Did they transport equipment?
Another thought: could it have been made in Germany FOR Japan? The prussian army had some bonds to the Japanese land forces. Any equipment intended for Japan that was on the production line at the outbreak of war would have been sized and reused if possible.
The plot thickens! As I pulled this off the scanner this morning I found that it was mailed in 1941. It is part of a set used for East Prussian relief. Not sure when the postcard was made but it was not mailed during the war.