German prisoners during WWII were let outside camps without US guards on the honor system. No one ever ran away!
The U.S. Entered WWII in 1941. Britain quickly asked the U.S. To help house prisoners of war, because Britain didn't have enough housing for them all. The U.S. Agreed, but they were sorely unprepared. During WWI, the U.S.
Only housed prisoners of war for a short time, and when they agreed to it during WWII they didn't think of all the logistics like food, clothing, and housing needs for the prisoners. Germans much preferred to be captured by the British and U.S. Instead of the Russians.
They were placed in 700 camps in 46 states. The U.S. Was careful to meet the guidelines of prisoners of war by the Geneva Convention. They were so lenient that the U.S. Actually let German prisoners off the camps without guards on the honor system. No German ever ran away.