My grandfather was wounded in WWI. My father served in the Air Force during the early years of the Cold War. And my Zen grand-teacher served in the South Korean Army during the Korean War.The tradition of Korean Buddhist monks serving in the military goes back at least to the time of Sosan Taesa, a 16th century Zen Master. At that time the official religion of the Chosun Dynasty in Korea was Confucianism, and Buddhism was (very mildly by western standards) persecuted by the government. For the most part this "persecution" consisted of ending the generous financial subsidies that Buddhism had previously enjoyed during the Koryo Dynasty, and the closing of the large urban temples. Buddhist monks and nuns were forced to leave the cities and fend for themselves in the countryside, among the people.
When the Japanese invasion occurred in 1592, Master Sosan requested, and received permission to raise an army to help defend Korea. Ironically, the Confucianist Emperor was fleeing in the face of the invasion as he granted permission to this Buddhist priest to stay behind and fight. Master Sosan's four most senior students became his lieutenants, and one of those students, Samyong, participated in negotiating the peace treaty to end the war. The invasion had been repelled. While the Chosun Dynastry would continue to favor Confucianism for the next three hundred years, there was less real persecution of Buddhism from the time of Sosan Taesa onward, in large part due to the undeniable contribution Buddhists had made, under his leadership, in the defense of Korea.
During the Korean War, Buddhists once again participated in the defense of Korea against a different kind of foreign invasion. Throughout Asia, Communist ideologues have insisted on misapplying Enlightenment era critiques of Christianity to such religions as Confucianism, Taoism, Buddhism, Hinduism, Shamanism, Shinto, etc. Never mind the fact that contacts with Eastern philosophies and religions played an important role in the European Enlightenment! In North Korea the suppression of Buddhism by the Communists was far more brutal, sweeping and effective than anything that occurred during the Chosun Dynasty.Today Buddhism in North Korea maintains the same kind of ghostly existence as Buddhism in Tibet. Meanwhile in the South Buddhism continues to thrive as one among many religions (in fact there are a great many different forms of Buddhism, for that matter!) that Koreans are free to practice and espouse as they wish, in part thanks to the sacrifices made by Buddhist monks such as Zen Master Seung Sahn.
For more on Sosan Taesa and his exploits both as a Zen Master and as a guerilla fighter, see the book Thousand Peaks: Korean Zen: Traditions and Teachers, by Mu Soeng Sunim, especially Chapter Ten. The cool picture of Zen Master Seung Sahn as a young soldier was found over at Paul Lynch's blog, Zen Mirror.