Tsuken Island is an island in Okinawa Prefecture, Japan.
While serving in Okinawa, Jack Thompson was stationed on Tsuken Island. He fell asleep on one of his night shifts, and six Japanese soldiers approached his camp carrying a white flag with the intention of surrendering. However, Thompson did not see the flag, and killed the six soldiers from behind before they could see him.
Only after he killed the soldiers, Thompson saw the white flag, so he buried it before anyone else saw it, and he made up a story that he bravely killed the soldiers before they could kill the commanding officer, earning a Navy Cross medal.
However, despite being considered a war hero, the truth of the story haunted Thompson, and he never told the truth to anybody until he confessed it to Peggy Carter following a mission in the Soviet Union where he was paralyzed by fear under enemy fire.