MILITARY ADVISORS IN KOREA: KMAG IN PEACE AND WAR by Major Robert K. Sawyer Edited by Walter G. Hermes CENTER OF MILITARY HISTORY UNITED STATES ARMY WASHINGTON, D.C., 1988 Library of Congress Catalog Card No. 62–60015

For general defensive planning, the Americans divided the
terrain along the 38th Parallel into six areas for analysis, and,
without attempting to consider probability factors, assigned each
zone a letter (A to F).27



Area A was the Ongjin Peninsula, covering
approximately twenty-six air-line miles of mountainous terrain
along the parallel. That portion of the peninsula occupied
by South Korean troops was an island insofar as the Republic
of Korea was concerned, for it was bounded on three sides by
water and on the north by the 38th Parallel. Strategically, the
area was of value only in that the possessor had a third-rate
warm water seaport and a secondary all-weather airstrip. Tactically,
possession of Ongjin Peninsula would be of value to the
North Koreans because it would release their troops from a mission
of containment; moreover, the peninsula could serve as a
base for a seaborne assault on the port of Inch’on. One ferry
crossing connected the eastern edge of the peninsula to the
mainland across Haeju Bay.

Area B covered approximately thirty-five air miles across the
Ch’ongdan area from Haeju Bay to the Yesong River. This terrain
was very mountainous along the 38th Parallel and northward,
but south of the line were foothills and flatlands. The
latter were suitable for the employment of armor, though tanks
would be channelized except in winter when the rice paddies
were frozen solid. The Yesong River, flowing from north to
south, seldom froze sufficiently to support troops or vehicles.
There was one good lateral road in this area (south of the
parallel) and six fair roads running north and south. A ferry and
a large double-track railroad and highway bridge spanned the
Yesong River, connecting the zone with the Kaesong area to the

Area C stretched for about thirty-one air miles along the
Parallel from the Yesong River to the Imjin River. The principal
town in this area was Kaesong, ancient capital of Korea. The
terrain was similar to that in the Ch’ongdan area and was suitable
for armor under the same conditions. There were three fair north-south roads and one good lateral road south of the parallel,
as well as large numbers of foot-paths and ox trails crisscrossing
the area. The primary railroad link between North and South
Korea passed through here. If held by an enemy, the zone would
provide an excellent tactical base from which to launch an assault
into the Sŏul district. Such an assault, would, however, be
greatly impeded by the Imjin River; although the stream occasionally
froze to a depth sufficient to support foot troops and
vehicles, a successful attack would have to include the capture
of two large single-lane railway bridges, one of which had been
converted for the use of wheeled and light tracked vehicles.

Area D, called the Uijongbu area, extended for some twentytwo
miles from the Imjin River eastward to include a northsouth
valley running between Sŏul and Wŏnsan, important east
coast seaport and rail center in North Korea. This ancient invasion
route contained a road and railroad connecting the lowlands
around Sŏul with the flatlands in the vicinity of Wŏnsan.
Although not in first-class condition, the corridor was the best approach to Sŏul from the north and was militarily important.
There was good observation both north and south of the Parallel
in this zone. One poor lateral road and numerous mountain trails
led east toward Ch’unch’on.

Area E ran from the Sŏul-Wŏnsan corridor approximately
thirty-six air-line miles to the eastern limitation of the Hongch’on
River valley where it crossed the 38th Parallel at Pup’yong-ni.
The terrain was mountainous and lent itself favorably to guerrilla
action, On each flank of the zone, minor valleys ran north
and south along the Choyang and Pukhan Rivers, which converged
at Ch’unch’on to become a tributary of the Han River.
Although a highway and railroad ran over the mountains from
Ch’unch’on to Sŏul, good roads in this zone were few. There
was an improved airstrip in the valley containing Ch’unch’on.
Laterally, a road wound deviously through the mountains toward
Kangnung, on the east coast.

The remaining twenty-nine miles—Area F—contained the
most rugged country along the 38th Parallel. Except for a few
miles of coastal plain, the terrain was wild and completely mountainous.
One good road ran along the coast; other roads in the
zone were hazardous and practically impassable during the winter
months. A railroad bed had been laid along the coast by the
Japanese, but while tunnels and concrete abutments were complete,
there were no tracks nor had bridges actually been built;
the coastal road followed the roadbed. One second class seaport
at Chumunjin and one airstrip at Kangnung posed the only strategic
targets; tactically, the zone lent itself to guerrilla warfare.
In view of the terrain, the ROK Army’s lack of equipment and
need for training, and the guerrilla activity in South Korea, the
Americans felt that it would not be practicable for ROK divisions
to deploy in formal defensive positions across the width of the
peninsula. It was likely, moreover, that any thrusts from the north
would occur in certain predictable areas; zones B, C, and D all
contained good avenues of approach. ROK Army officers believed
that the Uijongbu area was the key to the city of Sŏul,
and that an invasion, if it came, would be concentrated there.
The United States advisors therefore recommended a series of strong outpost positions blocking probable avenues of approach
as the best defense along the 38th Parallel.28

As Korean units replaced U.S. Army units along the border in
late 1948 and 1949, the ROK Army assigned sectors on the mainland
to the 1st, 7th, 6th, and 8th Divisions, and stationed the
Capital Division’s 18th Infantry Regiment (later the 17th) on
the Ongjin Peninsula. These units organized and maintained
strategic strongpoints, and covered less important areas within
each sector with foot or motorized patrols. As noted earlier, the
majority of units in each of these divisions remained well south
of the line, engaged in training or guarding installations. The
remaining ROK Army divisions—the Capital (less one regiment)
at Sŏul, and the 2d, 3d, and 5th in the south—and the
cavalry regiment, constituted the Republic of Korea Army Reserve.
In the event of invasion, the units on the Ongjin Peninsula
and west of the Imjin River would withdraw, leaving the western
sector with a natural defense line along the Imjin River north
to where the stream crossed the 38th Parallel. The reserve would
then: (1) counterattack; (2) reinforce the ROK 1st and 7th
Divisions; (3) reinforce the ROK 6th and 8th Divisions; or (4)
suppress guerrillas in the interior of South Korea, in that priority.
The U.S. Military Advisory Group believed that the ROK Army
could contain and repel an invasion, unless Chinese Communist
Forces participated, if it abided by this plan.

Like other U.S. installations throughout the world, the American
Mission in Korea had an alert and evacuation plan ready for
emergencies. This plan,29 labeled CRULLER, was designated to
safeguard the persons and property of all U.S. citizens and certain
designated foreign nationals in Korea in the event of internal
disturbances or of invasion from North Korea. It also provided
for their evacuation along with their property, if time permitted.
The plan was so drawn that it could be implemented as a joint
AMIK–KMAG plan or used by either element separately. The
senior KMAG G–3 Advisor was responsible for keeping the plan
up to date.

Map of The North Korean Invasion

24 SA Rept, KMAG, 15 Jun 50, sec. III, pp. 5–7.
25 Ibid., sec. V, p. 16, and an. X.
26 See ch. I, above.
27 SA Rpt, KMAG, 15 Jun 50, an. III, sec. I. Also see SA Rpt, KMAG, 31 Dec 49, an. 5.
28 See: (1) SA Rpt, KMAG, 31 Dec 49, sec. IV, pp. 24–25; (2) SA Rpt, KMAG, 15 Jun 50, sec. IV, p. 15.
29 P&O File 381 CR (14 Jul 49) R/F 7–28/867.