SOURCE AND LIMITATIONS

In war, battle casualties result from many complex factors which seldom, if ever, combine to produce identical situations for each type of campaign, each type of tactical operation, and, indeed, even for each type of tactical action. Some of these factors, which vary in significance, are the weapons employed and their relative firepower; the size and experience of opposing forces; the excellence of plan and tactics of battle; the type of terrain and advantage of position; and the tactical, strategic and logistical support provided. Disease cases, on the other hand, are more a product of exposure related to geography, climate, and season of year, while nonbattle injury cases result from external causes other than the hostile act of an enemy. The incidence of battle casualties, however, by particular operations and tactical actions, and of nonbattle admissions by type of operation, can often provide a basis for the projection of the combined effects of certain of these variables, which are important from both the tactical and logistical standpoints. In addition, certain operations of the same type, by one coincidence or another, produce battle casualty rates that are similar, and certain types of operations consistently average higher or lower battle casualty rates than do other types. For example, certain types of ground operations in World War II were observed to produce higher than average casualty rates (6). In preparing that material, research into division tactics did not go beyond the classification of ground operation for the entire division, and only counts of the wounded in action who lost time from duty were made available.

The preparation of these data has included research into the tactical action of the separate regiments in relation to the type of ground operation of the division as a whole. Casualty counts for these operations have been expanded to represent the total number hit: the killed in action plus all of the wounded in action, even those who were slightly wounded and who lost no days from duty and were CRO cases.

The operations classified here account for 93 percent of the total number hit (killed and wounded, including CRO cases) among U.S. Army troops in the Korean War. Of the final medical counts, therefore, 18,654 of the 19,353 killed in action, 72,926 of the 77,788 wounded-in-action admissions, and 12,468 of the 14,575 slightly wounded CRO cases are included in the divisional operations. Detailed data for nonbattle as well its battle casualties are included in appendix B (source tables B-5 through B-11), separately, for divisions, regiments, headquarters and service companies, division artillery, and for engineer, medical, and tank battalions, for every tactical division operation of the Korean War.

The chief sources used in determining the types of tactical actions and types of operations were the unit periodic operation reports, various staff journals, and other command and staff reports (7). These operations reports were usually prepared each day and covered a unit's combat operations for the previous 24-hour period. No attempt was made to go below regiments for the tactical action, and, consequently, a few selected were necessarily arbitrary, especially when more than one tactical action was given for the three infantry battalions of a regiment. In general, the selection involved nothing more than a determination as to which tactical action, on any particular day was most likely to have produced most, if not all, of the casualties in any single given regiment on the same day. Since reporting procedure at Army and division level followed the pattern of recording only the principal tactical activity in which a particular regiment was engaged in any 24-hour period, it was from these reports that final determination was made. The chronology of the various tactical operations, and the dates when U.S. Army divisions, their organic regiments, and attached separate regimental combat teams were committed or relieved, was documented more accurately and posed no special problems.

The classification of tactical operations was developed to classify all of the killed and wounded-in-action casualties sustained by each of the eight

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¹ Killed in action stated as number per 1,000 average strength per day.
² Main Battle Position such as defensive lines.
³ Less than 0.005 per 1,000 men per day.

U.S. Army divisions and the two separate regimental combat teams which served at one time or another in the Korean War. The types of operations and tactical actions reflect the character of U.S. Army divisional experience in Korea, which is, to a certain extent, influenced by quality of the various after-action reports. The types of divisional operations developed are offensive operations, pursuit and mopping-up, maintaining static defensive lines, limited operations from main battle positions, defensive (enemy offensive) operations, withdrawal operations, redeploying and regrouping, and corps or army reserve. The types of regimental tactical actions are attack, heavy resistance; attack, light resistance; airdrop, attack; assault river crossing; defense, enemy attack or counterattack; withdrawal and rearguard action; patrolling; establish, hold, or consolidate defensive positions; mopping-up or consolidating gains; movement or redeployment; and reserve.

The divisional operation covers an overall stated period of time and the regimental action represents day-to-day tactical activity within the overall divisional period. While most of these tactical actions pose no special problem of definition, some necessarily are slightly ambiguous. For example, "airdrop attack" includes not only the parachute drop but also ground action of whatever classification that might occur on the same day. The action "establish, hold, or consolidate defensive positions" includes the operation of outposts, security guarding, and, static defense on main battle positions, as well as the "holding" action on offense and defense. The only other less-well-defined action is"patrolling," and that includes ambush, reconnaissance, security, contact, and raiding parties.

OFFENSIVE OPERATIONS

The major U.N. offensive operations in Korea occurred within the first 16 months of the Korean War. These operations are distinguished from the limited objective attacks by relatively small forces (limited operations from main battle positions) in that each of the 11 offensives studied represents a major United Nations Forces effort against the enemy involving more than one division over a wide front. In two instances, the experience of a single U.S. Army division is shown. The first one (Inchon

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¹ Wounded in action and admitted to a medical treatment facility, stated as admissions per 1,000 average strength per day.
² Main Battle Positions such as defensive lines.

landing) involved the 1st U.S. Marine Division and the 7th U.S. Army Division; the second (Operations Nomad-Polar) involved a force of two Republic of Korea divisions along with the 24th U.S. Army Division, in both, data are given for the respective U.S. Army division alone. Although these data cover only U.S. Army experience, every action included both Republic of Korea and other United Nations Forces as well.

In these 11 offensive operations, six U.S. Army divisions and two separate regimental combat teams contributed 43 division-periods, averaging 14.7 days and totaling 25,737 men hit. For all divisions, tables 20 and 21 give the distribution of divisional KIA (killed in action) and WIA (wounded in action,) admission rates, respectively, expressed as cases per 1,000 average divisional strength per day over the entire period of participation of each. These rates ranged from 0.02 to 1.45 for killed in action and from 0.17 to 7.40 for wounded in action. Frequency distributions for divisional WIA-CRO rates are not shown because they represent neither unit losses for which replacements would be required nor admissions to medical treatment facilities from which hospitalization and evacuation requirements originate. Figure 4, however, presents the counterpart of these distributions for the total hit, which includes the WIA-CRO cases.

The average divisional rates for major offensive operations as shown in table 22 are 0.36 KIA, 0.21 WIA-CRO, and 1.80 WIA-admissions for a total of 2.37. These are weighted mean rates obtained by weighting each individual divisional rate by the proportion of the total man-days for the specified type of operation which it represents. The arithmetic means are slightly higher: 0.39, 0.25, and 1.93, respectively, totaling 2.57 hit per 1,000 men each day. All of the rates given in table 22 are weighted mean rates, as they are in all of the succeeding tables. When statistical comparisons are made on the total hit between different types of operations as well as between operations of the same type, the differences are highly significant. However, the mean rates of certain pairs- for example, Operations Ripper vs. Rugged; the Inchon landing vs. Operation Detonate; and the January 1951 U.N. counteroffensive vs. Operation Dauntless- do not differ significantly (P>.05). Neither do the means differ for the two highest division rates, which represent the last two major offensives of the war and surpass all others for any type of operation studied. This variation might indicate that, while very different, rates are being averaged, nevertheless certain instances do occur in which some uniformity exists. Table 23 presents weighted regimental rates per 1,000 men per day for the

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various regiment tactical actions performed during the parent divisions' offensive operations. Needless to say, these rates for each separate type of action differ significantly between the several types of operations with, but one exception. The mean hit rate of 11.13 for the airdrop attack of the 187th Airborne Regimental Combat Team at Munson-ni in support of Operation Ripper (table 23) does not differ siguificantly from that (12.33) for the jumps on the Sukchon-Sunchon area north of Pyongyang to trap retreating North Koreans during the Eighth U.S. Army's operations of pursuit (table 24). However, if the relative distribution of killed and wounded is considered, a significantly higher pro-

23

¹ Inclusive dates within which one or more U.S. Army divisions (including attached separate Regimental Combat Teams) contributed combat days to the indicated operation.
² Slightly wounded-in-action cases treated on an outpatient basis, usually at an aid station, and returned to duty before the close of the morning report day.
³ Wounded-in-action and admitted to medical treatment facility.
⁴ Stated as cases per 1,000 men per day.

¹ Slightly wounded-in-action cases treated on anoutpatient basis usually at an aid station, and returned to duty before the close of the morning report day.
² Wounded in action and admitted to a medical treatment facility.
³ Stated as cases per 1,000 men per day.

24

¹ Slightly wounded-in-action cases treated on anoutpatient basis usually at an aid station, and returned to duty before the close of the morning report day.
² Wounded in action and admitted to a medical treatment facility.
³ Stated as cases per 1,000 men per day.

portion of those hit at Sukchon-Sunchon were killed in action. As was the case with the divisional rates, certain pairs of regimental tactical action rates during divisional offensive operations are found to be similar; for example, attack light resistance, and mopping-up.

PURSUIT AND MOPPING-UP OPERATIONS

Operations of pursuit were easily defined and resulted from the complete disintegration of the North Korean Army in retreat. While the bulk of their battered army fled north, fragmented units cut off from escape formed pockets of resistance in the hills of South Korea. Both of the areas north and south of the 38th Parallel required large sweeping actions in the pursuit and mopping-up of these enemy elements. The Iwon landing and pursuit by the 7th U.S. Army Division, although a part of the general pursuit in North Korea, was considered separately to evaluate any differences that the amphibious character of this action may have produced. The three operations represent 11 division-periods averaging 27.5 days in length. The distributions of the KIA and WIA admissions (tables 20 and 21) show a high concentration below 0.20 and 0.50, respectively. The weighted mean rates for these operations are given in table 25 and differ significantly. The pursuits in North Korea against the main forces produced the highest rates. Since the landings on Iwon Beach and the movement north were virtually unopposed during the first few days, this latter operation resulted in relatively light casualties. The regiment tactical actions during division pursuit operations (table 24) show that more, than one-half of the regimental-periods were spent in patrolling and establishing and holding defensive positions, the former to locate the fleeing enemy and the latter to block his escape. All but two of the regimental rates for tactical actions in pursuit are lower than the corresponding regimental rates for division offensives: airdrop attack, as previously mentioned, and reserve status. The latter phenomenon resulted from the absence of any well-defined front, and units in reserve often found themselves under attack from the bypassed enemy.

MAINTAINING STATIC DEFENSIVE LINES

The static type of defensive line in Korea developed from arbitrary phase lines which more often followed the natural features of terrain such as river and ridge lines. These lines, delineated major objectives on offense and composed secondary lines of resistance on defense. When it became apparent that the thinly held line north of Seoul was disintegrating beneath the weight of a major Chinese Communist Offensive, U.N. Forces were ordered to withdraw, from North Korea to Line "D," beginning on 5 January 1951. This line ran from the Yellow Sea in the west through Pyongtaek, northwest through Wonju and just north of Samchok on the east coast (fig. 5). During most of this time, main Chinese Communist Forces pressure was on

25

26

¹ Inclusive dates within which one or more U.S. Army divisions (including attached separate Regimental Combat Teams) contributed combat days to the indicated operation.
² Slightly wounded-in-action cases treated on an outpatient basis, usually at an aid station, and returned to duty before the close of the morning report day.
³ Wounded-in-action and admitted to medical treatment facility.
⁴ Stated as cases per 1,000 men per day.

¹ Inclusive dates within which one or more U.S. Army divisions (including attached separate Regimental Combat Teams) contributed combat days to the indicated operation.
² Slightly wounded-in-action cases treated on an outpatient basis, usually at an aid station, and returned to duty before the close of the morning report day.
³ Wounded-in-action and admitted to medical treatment facility.
⁴ Stated as cases per 1,000 men per day.

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¹ Slightly wounded-in-action cases treated on anoutpatient basis usually at an aid station, and returned to duty before the close of the morning report day.
² Wounded in action and admitted to a medical treatment facility.
³ Stated as cases per 1,000 men per day.

Republic of Korea elements and the 7th U.S. Army Division from Wonju eastward to Checon. During the next 8 months, from February through September 1951, other major lines, designated BOSTON, KANSAS, GOLDEN, NO NAME, WYOMING and KANSAS/HAYS, reflected the main defensive positions of U.N. Forces back and forth across the map of Korea. After the last major U.N. offensives in October 1951, which advanced the U.N. Forces to more favorable terrain, the lines became more static and were supported by a series of strong outposts forward of the main lines. The latter became known as the "Outpost Line of Resistance," and the main line was designated "Main. Battle Position." Attacks on single strong points, such as Bloody Ridge, Heartbreak Ridge, Porkchop, and Old Baldy on the outpost lines, and other limited actions to move or improve positions on the main defensive lines, were omitted from operations in this class and placed in the class of limited operations from main battle positions. The last main battle positions which remained more or less static to the end of the war in July 1953 were Line JAMESTOWN on the western front, Line MISSOURI on the central front, and Line MINNESOTA on the eastern front. Figure 5 shows the final demarcation line as of 27 July 1953.

These operations (table 26) had the lowest rates of any active operation; only the passive operations of redeploying, regrouping, and reserve were smaller. The distributions in tables 20 and 21 show the bulk of the rates below 0.20 KIA and 0.50 WIA, respectively. The highest rate, 0.76 hit per 1,000 men per day, occurred for the KANSAS/HAYS line in the X Corps sector because most activity occurred there. Advances by X Corps tended to straighten and shorten U.N. lines, and in addition, this area was more remote from the Kaesong neutral zone. There are no large differences between the average rates for the individual lines although the numbers are so large that any small differences in the rates are highly significant statistically. The number with similar rates- for example, Line D and No Name; Kansas and Missouri; Golden, Jamestown, and Minnesota- indicate that one might find less variation in this type of operation. The static, nature of these operations is also reflected in the fact that less than 1.5 percent of all of the regimental time was spent either in defending (defense and withdrawal actions) against enemy attacks on the main line or in counterattacking (attack actions) to restore positions (table 27). Almost three-fourths of the time was used for patrolling and holding the main positions, while the balance of time was used for redeploying, regrouping, and reserve. The average daily regimental rate of 0.63 hit per 1,000 was also the lowest rate experienced for any type of active operation.

LIMITED OPERATIONS FROM MAIN BATTLE POSITIONS

Beginning in July 1951, with the start of peace talks at Kaesong on the 38th Parallel, no large-scale operations were undertaken by U.N. Forces throughout the summer until October 1951. Limited operations, with relatively small forces of regimental size or smaller, were undertaken, however, to keep the

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¹ Inclusive dates within which one or more U.S. Army divisions (including attached separate Regimental Combat Teams) contributed combat days to the indicated operation.
² Slightly wounded-in-action cases treated on an outpatient basis, usually at an aid station, and returned to duty before the close of the morning report day.
³ Wounded-in-action and admitted to medical treatment facility.
⁴ Stated as cases per 1,000 men per day.

enemy off balance and to seize dominating terrain, thereby improving the defensive positions. On Line WYOMING in the I Corps area, (Western front) closest to the Kaesong neutral zone, the dominating terrain of the Sobang Mountains was obtained in action during the first 4 days of July 1951. Thereafter, activity was limited to raids and to two operations designed to sweep the enemy from the Corps front. On Line WYOMING, in the IX Corps Sector (Central front), several small-scale operations secured new positions on the line in addition to tank-infantry raids into the "Iron Triangle." Line KANSAS/HAYS in the X Corps sector (Eastern front) was furthest from the Kaesong neutral zone and a large portion of U.N. activity was centered there. The battles for Bloody Ridge from Line KANSAS sector of the line and Heartbreak Ridge on the HAYS sector of the line are the most notable and were largely responsible for the high division hit rates of 6.49 and 5.51, respectively, as given in table 28. When the rates are related to the specific regiments of the U.S. Army 2d Infantry Division that fought there, very high regimental rates are obtained. The 9th Infantry Regiment on Bloody Ridge had average daily rates of 152 KIA, 201 WIA-CRO, and 16.49 WIA-admissions, totaling 22.02 men hit per 1,000 troops exposed over a 10-day period. The 23d Infantry Regiment fought for Heartbreak Ridge almost twice as long as the 9th Infantry Regiment on Bloody Ridge, and sustained average daily rates of 3.14 KIA, 0.30 WIA-CRO, and 11.48 WIA-admissions, totaling 14.92 men hit per 1,000.

Again, after the last two major U.N. offensives in October 1951, action was reduced from large military operations to company and platoon patrols and raids. More often, the battles raged over single strong points or outposts forward of the main lines which, themselves, remained more or less static to the end of the war in July 1953. A total of 16 limited operations (see tables B-5 through B-11, appendix B) involved U.S. Army troops from Line JAMESTOWN, notably the several battles for outposts on Porkchop Hill and Old Baldy, and the defense of outposts Kelly, Carson, Elko, and Vegas, among others. The respective highest average, daily regi mental rates for any individual limited operation occurred on Line JAMESTOWN. The highest average daily regimental KIA rate appeared during the fourth battle for Old Baldy, 18-21, September