The battle of Okinawa commenced 1 April 1945 and ended 22 June that year. This battle had one of the highest casualty rates of World War 2. Ernie Pyle, who was killed in action 18 April 1945, told the following story in one of his reports from that battle. It appeared in The Argus, Tuesday, 24 April 1945, page 2.
At one of our halts word was passed back that we could sit down but not take of packs. From down the line came the music of a French harp and a ukulele playing, “You are My Sunshine”. When it was finished the marines would call back request numbers, and the little concert went on for 5 to 10 minutes out there in the Okinawa fields…. [a bazookaman, William Gabriel played the harmonica, and Lieutenant ‘Bones’ Carsters played ‘ukulele’] … He strummed the cords on the sort of ukulele common to Okinawa. It has three strings and the head is always stretched snake-skin. It gives you the willies just to look at one.”
The instrument referred to was probably a sanshin.