I was reading the manga Cat Shit One, also called Apocalypse Meow. In one of the historical sidebars listed some of the ROK divisions that participated in the Vietnam War. The Yellow Tiger, Blue Dragon and White Horse or Stallion divisions were South Korea's contribution to the Vietnam War. Some of the other names for ROK units are Iron Wall, Golden Bat, Angry Wave, Pegasus and Eagle. In the case of the White Horse division the name cane be traced to a battle in the Korean War where the 9th div was able to beat back an assault by chi-com troops. You can read the history of the Battle of White Horse Mountain here. Below is a photo of White Horse Mountain.