During WWII my father was stationed in the Philippines but after the war ended he was sent to Korea to help establish the new government. He was there from October 1945 to September 1946. I found this among his belongings.

The bill is still crisp. It has only one fold on the right bottom quarter. It is not graded and I am not an expert at determining quality. For being printed in 1945 I think it still looks very good. My understanding is that the A block series is harder to find than the B.

From Wikipedia:

A yen (A, A en) was a colloquial term used to refer to a form of military scrip used in post-war US-Occupied Japan, Korea, and Okinawa from September 7, 1945, to July 21, 1948. They are notable for being the first" Military Payment Certificates" (In Korea) given after World War II had ended.[1]

Both "A" and "B yen" scrip in denominations from 10 sen to 100yen were printed in 1945.

The United States military used these as payment certificates, while the civilian population used "B Yen"scrip as currency.[3] "A yen" scrip was used as general currency in Korea from September 7, 1945, to July 10, 1946.[2] It was used for military use only from July 19, 1946 to September 30, 1946.

A type yen are much rarer because they had to be exchanged, within a specific time period, for the newly issued Military Payment Certificates that replaced it. Once exchanged the A type was then worthless and destroyed. (Cited from: https://www.cointalk.com/threads/us-military-currency-japanese-occupation.232762/)