They did prove to be fearsome opponents by the Vietcong during
the Vietnam war. ROK sent three divisions of troops to Vietnam
beginning to help the Americans fight against North Vietnam. The
"White Horse," "Blue Dragon," and the "Tiger" divisions totaled
more than 300,000 men over a twelve year period.
Below is a quote from wikipedia on the ROK marine corp:
"Most of the operations never exceeded battalion-size, but they
also conducted divisional size operations. Before conducting
missions, Koreans laid out their plans much more carefully than
their allies, with greater fire discipline, the very effective use
of fire support, and better co-ordination of sub-units. They also
had to their favor the distinguished combat leadership of the
company and platoon commanders. During village searches, ROK
soldiers would subject the settlement to a series of detailed
sweeps while interrogating subjects on the spot. By comparison,
American units tended to favor a single sweep followed by a removal
of all civilians for screening. Such a painstaking approach
certainly paid dividends in terms of weapons seizures and reduced
VC activity in ROK areas. Koreans quickly learned pidgin Vietnamese
language; for fear that most Vietnamese translators were spies for
Vietcong and NVA. Koreans also had better field intelligence than
their American counterparts. Koreans conducted counterinsurgency
operations so well that American commanders felt Korean AOR was the
safest. This was further supported when Vietcong documents captured
after the Tet Offensive warned their compatriots to never engage
Koreans until full victory is certain. In fact, it was often that
the NVA and Vietcong were ambushed by Koreans and not vice
versa.
Their most notable operations in Vietnam were "Operation Van Buren"
and the Battle of Hoi An. During "Operation Van Buren", a ROKMC
platoon of about 13 soldiers wiped out an elite North Vietnamese
Army regiment, resulting in only 2 Korean casualties while more
than 400 NVA soldiers were killed. The initial gun battle had
devolved into bloody hand-to-hand combat. The ROKMC boasted an
overall kill ratio of 25-to-1 in the Vietnam War"
