Foreign Relations of the United States, 1969–1976, Volume XIX, Part 1, Korea, 1969–1972

53. Memorandum From Laurence E. Lynn, Jr., of the National Security Council Staff to the President’s Assistant for National Security Affairs (Kissinger)¹

Washington, February 26, 1970.

SUBJECT

• ROK Force Capabilities

The ROK force capabilities remain subject to considerable disagreement for postures which reduce both ROK and U.S. active forces in Korea. The JCS claim, for example, that Posture 3 outlined in the Korea “issues” paper, could neither “stem” a North Korean attack nor “delay” a combined NK/CPR attack.²

This memo summarizes the Korea Study’s assessment of this problem using historical experience, wargame simulation, and force effectiveness comparisons.

The conclusions are that:

• —a decision to withdraw a U.S. division and to maintain an 18 or 19 division ROK force structure involves no military risks of any significance.
• —we need not “modernize” the entire ROK 18 or 19 division force structure to enable them to defend themselves against the present or likely future North Korea force structure.

Posture 3

The ground forces included in Posture 3 are:

• —One U.S. infantry division with about 15,000 U.S. combat personnel and 15,000 support personnel in Korea.
• —Sixteen ROK active divisions with modernized combat and support equipment. About 13,200 men per division. Including combat support, these divisions will yield a total combat force of 429,000 men.
• —Five ROK ready reserve divisions (3,000 fulltime personnel per division) and seven ROK rear area reserve divisions (1,500 fulltime personnel per division). When activated, which would take 15 days for the ready reserve and 30 days for the rear reserve, those divisions would add 135,000 men to the ROK force structure. In addition, the ROK have a 500,000 man armed militia which they plan to increase to 2,000,000 men in strength.

These forces would be deployed forward, with the U.S. division and 16 active ROK divisions positioned north of Seoul in prepared defensive positions along the invasion routes from North Korea. The reserve and rear area divisions would be largely south of Seoul and could³ not enter the conflict at its onset.

The threat to South Korea would consist of either:

• —Twenty-five North Korean infanty division equivalents (the North Koreans have only 19 organized infantry divisions) with a strength of 9,200 men per division. Including combat support, the North Koreans could field a total combat force of 281,000 men.
• —Forty-five NK/CPR division equivalents (including the 25 NK divisions) for a total combat and combat support force of 666,000 men.

Against North Korea, the attacking force, assuming careful prior planning and complete surprise, would consist at most of about half the North Korean force or 12 combat divisions. U.S. field commanders judge that this force would probably attack along the three principal invasion routes used in 1950 with the bulk of the force (about six divisions) targeted on Seoul.

Historical Experience

Our experience during the Korean War offers a few guides to assessing these U.S./ROK force capabilities and the force requirements for deterring a North Korean attack.

In early 1950, the ROK forces consisted of eight light infantry divisions (85,000 combat personnel) poorly organized for defense against a conventional attack from North Korea:

• —The ROK forces were outnumbered 1.5 to 1 overall and 2.0 to 1 along the DMZ.
• —The ROK defenses were poorly prepared and about half of the ROK force was engaged in anti-guerrilla operations south of Seoul.
• —The total investment in ROK equipment totaled only $50 million. As a result, the North Korean force were stronger numerically than the ROK in nearly all categories of equipment. ROK logistical supplies were adequate for less than 15 days of combat operations.

With this numerical and qualitative superiority, the North Koreans were able to successfully defeat the ROK forces in 1950.

This force balance changed measurably during the remainder of the war. During 1951, the NK/CPR Spring offensive and the UN counter-offensive showed that:

• —The NK/CPR forces of over 800,000 men could be held by a UN force of 535,000 men including about 320,000 ROKs.
• —The UN forces successfully counter-attacked with a force of about 550,000 men against a combined NK/CPR force of about 700,000 men.

In both cases, the UN’s combat forces engaged in the conflict were about equal to the enemy’s in spite of the great disparity in the sizes of their overall forces. While the UN consistently supported over half of its forces in combat, the NK/CPR rarely kept more than one-third of its forces engaged because of its inferior logistical support. With equal combat manpower, the UN forces superior firepower and combat support gave it a substantial advantage.

Judging from this experience, an ROK force with a comparable logistical and equipment advantage could hold an all-out North Korean attack with forces substantially smaller (10 ROK divisions would suffice) than the attacking force and defeat it with an equal-sized force. With a Posture 3-size force, the ROK could field 430,000 men north of Seoul of whom 215,000 could be engaged and supported in combat. Within a month, the ROKs could further increase this combat force to 275,000 men. The attacking NK force would be about 180,000 during the initial offensive but only 115,000 on a sustained (more than one month) basis.

Therefore, even with a Posture 3 force, the ROKs could maintain a clear superiority over North Korea’s forces. The U.S. forces in Korea and reserve ROK divisions would not be needed; but, if engaged, would further enhance the ROK advantage.

Wargame Simulation

To draw the implications of this historical experience modified for current force capabilities, the Army has developed a wargame which simulates conflict in Korea under a variety of conditions. Because the JCS estimate that 21 U.S. or ROK divisions would be required to defend against a NK attack, the wargame was first used to test this estimate. The Army found that an initial attack by 21 of the 25 NK divisions supported at ROK standards could be held north of Seoul for at least 30 days by 20-2/3 ROK divisions and 1-1/3 U.S. divisions if the attack were a complete surprise and ROK forces were not in defensive positions. However, a number of the Army’s assumptions were unrealistically conservative.

• —The NK could not attack with 21 of the divisions in their force structure. The NK could support no more than half (12 divisions) of their force in combat. Moreover, because of the North Korean’s need for a reserve against amphibious attack, the intelligence community’s estimate is that a NK attack would consist of only 6–9 divisions.
• —The logistical capabilities of the North Koreans are substantially less than the ROK or the U.S. forces. The average ROK combat soldier is backed by twice as much support manpower and would receive four times the logistical support of a NK soldier. The relative advantage of U.S. forces is even greater.
• —The ROK forces are now deployed in strong defensive positions along the invasion routes from North Korea. All 18 ROK divisions are now deployed north of Seoul.

Incorporating more realistic assumptions into the Army’s wargame, it becomes apparent that about six ROK divisions could meet an NK attack initially and that as few as 9–12 divisions could hold on a sustained basis. Under Posture 3, the ROK’s 16 active and modernized divisions could more than meet this requirement.

Force Comparisons

To check this analysis, the ROK capabilities were compared in detail with the expected NK and NK/CPR threat to determine if there were structural or equipment deficiencies in the ROK forces that would limit their performance or require modernization.

The force comparisons considered for each type of weapon:

• —The aggregate number of weapons by type in each combat force, i.e., the number of rifles held in the ROK and NK force structures.
• —The capabilities in combat of each major weapon, i.e., the relative effectiveness of a U.S. M–16 rifle and a NK AK–47 under combat conditions given the maintenance, supply, and doctrine governing use of the weapons.
• —The overall combat effectiveness ratio between ROK and NK or NK/CPR weapons systems considering the quantity, quality, and support of each major weapons systems.

From such comparisons, it was obvious that the present ROK force of 18 unmodernized divisions is stronger than the NK force in almost all major weapon categories. Moreover, this ROK superiority would be retained, even without⁴ modernization and with a considerably reduced active ROK force, for example, in Posture 3:

• —The ROKs have a definite edge in rifles, rockets, recoilless rifles, trucks, and communication equipment over the NK forces.
• —The ROKs are about equal in machine guns, mortars, artillery, tanks, and self-propelled assault guns.

Thus, without modernization, the ROK forces are more effectively equipped than the North Koreans. With the modernization envisaged under Postures 2 to 5, the ROK’s relative edge would be greatly increased.

• —Replacement of the M–1 rifle with the M–16 would double ROK firepower and further increase their advantage over the North Koreans.
• —Provision of more artillery and tanks would give the ROK a definite edge whereas they are now only equal to the North Koreans.
• —Better transportation and communications would facilitate ROK redeployment of their forces following a surprise attack. Although the ROKs have 3.5 times as many trucks as the North Koreans, the terrain in Korea makes lateral movement difficult.

However, these improvements, while desirable, are not necessary to maintain adequate defenses against North Korea unless extensive Chinese support for the North Korean forces is expected or the Soviets (North Korea’s chief supplier) prove willing to completely modernize the NK forces over the next five years.

Overall ROK Capabilities

These three independent analyses tended to corroborate each other in indicating that:

• —An ROK force of 12–14 unimproved divisions could probably hold an all-out North Korean attack. With a larger and improved ROK force now envisaged, the ROKs could defeat the North Koreans and at least attempt a march North.
• —An ROK force of 16–18 improved divisions could hold a combined NK/CPR attack for at least 30 days north of Seoul.

Based on these estimates, Posture 3 with 16 improved ROK divisions could easily defeat a North Korean surprise attack and at least hold a combined NK/CPR attack in which the Chinese entered within 15 days the largest force they could field and support. Against either threat, there is little or no military need for U.S. ground forces in Korea, with even the current unimproved ROK force structure. If the ROK force were built up to the 19 division modernized level, as the JCS suggest, the ROKs could attack North Korea with complete confidence and expect to hold on even if China entered the conflict. If the U.S. then introduced substantial forces, the ROKs could hope to defeat even a combined NK/CPR force and reunify Korea.

1. Source: National Archives, Nixon Presidential Materials, NSC Files, Box 541, Country Files, Far East, Korea, Vol. II, 10/69–5/70. Secret. Sent for information. A copy was sent to Haig. Kissinger initialed the memorandum on March 9 and added “Good report.”
2. See Document 52.
3. A handwritten notation changed “would” to “could.”
4. Kissinger underlined this word.