Some of the American prisoners who were interned at Camp O'Donnell were sent to Fort Stotsenburg and were forced to perform menial labor for their Japanese conquerors. These prisoners were considered the lucky ones as the others who remained in O'Donnell or Cabanatuan were moved aboard freighters to Japanese slave labor camps in the home islands. The Japanese refused to mark these vessels with the appropriate insignia, and many of them fell victim to American submarines, whose crews had no idea that the enemy ships they sent to the bottom carried fellow Americans aboard.