 The regiment was split into three groups for the attack . Three battalions acted as <unk> for the 5th Division on land while two more battalions conducted the landings in Imwonjin . This 2 @,@ 500 man force reassembled and then led the North Korean units south . In the meantime , the 3rd Battalion , 766th Regiment was detached and sent on a mission to infiltrate Pusan . Paired with additional support , it formed the 600 @-@ man 588th Unit . 588th Unit was tasked with raiding Pusan harbor , destroying vital facilities to make it impossible for UN forces to land troops there . However , the troop transport carrying the 588th Unit was discovered and sunk by United Nations ships outside Pusan harbor the morning of June 25 , destroying the 3rd Battalion . 
