Sen Or Yuan Or Yen ?

Sen is the decimal of the Yen (like cents is to the US Dollar). The military aspect is the American occupation of Japan after 1945. The sen character èA means money in Chinese.

Yuan is Chinese. Yen is Japanese. Both are the same: š¢

Bank of China and Bank of Communications are both still around in China. They don't print banknotes anymore. The Renminbi is the official currency of the People's Republic of China. It still uses the Yuan character.

I am assuming these notes were picked up by an American serviceman who brought back these souveniours.

Hope this helps!

The "military currency" notes were issued during and after the WWII Allied occupation of Japan. "Allied Military Currency" was also issued for France, Germany and Italy. They are the civilian counterparts for the "Military payment certificates" you might be familiar with. MPCs were for use by the occupying military forces; AMCs were for the civilian populations living in the occupied countries.

The combination of Japanese occupation during WWII and the Chinese Civil War saw the Chinese yuan collapse in value. By the time the Nationalists lost the mainland, the Nationalist yuan was effectively worthless, and the reconstituted regime in Taiwan declared all the old money invalid to prevent the Communists from flooding the island with fake notes printed from captured plates. So the notes have zero "face value". Their collector value is relatively low, too, since many examples survived in hoards and caches or were taken with them by refugees fleeing the conflict. They're the sort of notes my local coin dealer has in his "$1 each" bucket.

some corrections on the Chinese characters, hope they could be shown right:
Ç® or åX means money, here it may mean "coin".
Ôª or ˆA means dollar.
The two ROC banknotes are common ones and usually worth 1$ each.