 During the planning for the invasion of South Korea in the years before the war , the North Korean leadership began to create large numbers of commando and special forces units to send south . These units <unk> South Korean authority before and during the war with terror campaigns , sabotage and inducing rebellions in ROK military units . Hundreds of commandos were sent to South Korea in this fashion , and by the end of the war up to 3 @,@ 000 of them had been trained and armed . During this time , North Korean leadership also ordered the creation of large conventional units to act as advance forces for the actual invasion . The 766th Unit was formed in April 1949 at the Third Military Academy in <unk> , North Korea . The academy was specially designed to train commandos , and the 766th was originally designed to supervise North Korean light infantry ranger units . Over the next year , the 766th Unit received extensive training in unconventional warfare and amphibious warfare . During this time , the unit was expanded in size to 3 @,@ 000 men in six battalions . 
