Ground combat operations during the Korean War provided U.S. Army planners with an extensive array of lessons learned regarding the troops, tactics, and equipment involved in that conflict. In many cases, the lessons led to changes that had a profound impact on the Army that would enter the Vietnam conflict just over a decade later. In fact, some residual effects of Korean War changes can still be seen – in terms of Army unit structure, organization, and even equipment – in the American land force of the early 21st century.

The tragic fact is that the North Korean invasion south across the 38th parallel in June 1950 caught the U.S. Army relatively unprepared in terms of the troops, tactics, and equipment necessary to meet the assault.

An excellent example of this can be seen in the area of troop strengths. At the time of the initial invasion by North Korea, U.S. ground force strength was comprised of 10 U.S. Army divisions (in stark contrast to the Army’s 1947 goal of a 25-division structure) and a U.S. Marine Corps division. Of the 10 Army divisions, the only Army unit at full strength was the 1st Infantry Division, which remained in Europe to blunt any possible Soviet aggression on that continent. The other units were manned significantly below their wartime strength. In fact, to maintain even this small quantity of active combat units while staying within imposed manpower size limitations, the Army had been forced to remove a full battalion from each regimental structure.

To make matters worse, the four divisions located in Japan, closest to the fight, were filled in many cases with new recruits who had joined the units following World War II, had seen no combat, and had limited field training.

All in all, the necessity for extensive mobilization and commitment of Army Reserve and National Guard forces early in the Korean conflict helped galvanize the structural planning that would lead to the Armed Forces Reserve Act of 1952, a statute that provided much of the foundation for “Total Army” and “One Army” thinking that remains such a critical part of U.S. defense planning.

By war’s end, the U.S. Army ultimately sent a total of eight divisions to Korea: six  regular Army divisions and two National Guard divisions. However, it was the end of 1951 before the initial National Guard division (45th Division) arrived for action, with the second National Guard element (40th Division) arriving at the end of January 1952.

Other Reserve component ground forces also saw service in Korea. One U.S. Army Reserve history notes that 14 separate Organized Reserve Corps (ORC) battalions (the ORC was later renamed Army Reserve), 40 separate ORC companies, plus an undetermined number of individual ORC members were sent to Korea. The seven Medals of Honor (five awarded posthumously) earned by ORC members stand as just one measure of their contributions in combat.

All in all, the necessity for extensive mobilization and commitment of Army Reserve and National Guard forces early in the Korean conflict helped galvanize the structural planning that would lead to the Armed Forces Reserve Act of 1952, a statute that provided much of the foundation for “Total Army” and “One Army” thinking that remains such a critical part of U.S. defense planning.

Along with the training issues surrounding both active and Reserve component U.S. forces came the need for planners to address training requirements on an international basis.

U.S. Army historical reviews of the training situation reflect that the most desirable course of action would have been to employ all United Nations (U.N.) contingent units exactly as similar U.S. forces were employed. Unfortunately, that wasn’t always possible, as described by military historians. While the majority of reviews stress that most U.N. units were capable of executing the same missions assigned to U.S. forces, a few have added that this combat capability occasionally required additional training in rear areas or the selective assignments of critical offensive and defensive missions.

Planning support for an international military force extended well beyond unit capabilities and training to address issues as unique as national differences in meal customs and taste. Clothing was another national discriminator, with U.S. logisticians having difficulty fitting some foreign contingent members with the heavy U.S. field clothing and shoes demanded by the harsh Korean climate.

Korean War tactics and equipment tend to go hand in hand. The use of armored tank support provides the first case in point.

While some see it as a conundrum ranking with “what came first: the chicken or the egg?” most agree that it was only the arrival of actual tank hardware that allowed the ground force to develop the optimized tactics, techniques, and procedures for its employment on the Korean peninsula.

According to one historical examination prepared by the U.S. Army Armor Center and School, following North Korea’s invasion of South Korea, “The infantry divisions that had been on occupation duty in Japan immediately went into action in Korea, but they did not have their organic medium tank battalion or regimental tank companies. In fact, only a few light tank companies equipped with obsolescent M24 tanks were available in Japan. Initially, it was thought that the lack of tanks would not be a major drawback because the terrain in Korea, which is rugged and mountainous, with a few level areas covered by marsh-like rice paddies, was not considered suitable for their employment.”

One of the primary reasons that the divisions in Japan lacked any armor beyond their M24 Chaffee light tanks was the earlier decision that Japan’s infrastructure of road and bridge networks would not support heavier armor. It was a costly decision for the U.S. forces initially committed to action on the ground in Korea.

The Fort Knox historical synopsis elaborates on this point by adding, “The North Koreans used tanks, however, and on July 5, 1950, Task Force Smith, the first U.S. unit from Japan, was overrun by 31 Russian-made T-34 tanks. The North Koreans continued to employ their tanks with devastating effect, since the U.S. forces had almost no tanks with them to stop them.”

Moreover, even after U.S. forces did begin receiving heavier M4 Sherman medium tanks (where the first medium-weight armor attempted to support 24th Division soldiers who were trying to hold at the Kum River line), it was evident that the standard 76 mm main gun on the M4A3 and M4A3E8 Sherman was seldom overwhelming or even adequate when matched against the armor and ballistics package of the T-34.

The eventual arrival of both M26 Pershing and M46 Patton medium tanks helped to shift the armor balance in favor of U.S. forces while reinforcing the arguments of those who favored “heavier” tracked armament.

The Armor School’s Korean retrospective concludes that “The lessons of World War II, that tanks are necessary to fight other tanks and to spearhead offensive operation, were reemphasized. It was further demonstrated that armor is able to operate in terrain that is generally thought unsuitable for tank employment. The Korean Campaign also supported the contention that when one force has effective armor and the other does not, the force without effective armor will lose.”

In addition to these tank lessons, the obvious viability of tracked systems in Korean terrain was such that a plethora of battlefield support weapons were soon employed on tracked or semi-tracked weapon carriages. Examples ranged from the M16 series “Quad .50s” and M19 twin 40 mm up to self-propelled artillery systems like the M7 howitzer motor carriage with 105 mm howitzer and M41 howitzer motor carriage with 155 mm howitzer. Both of these latter systems provided significant mobility and operational speed advantages over their towed counterparts.

The proud artillery lineage spawned by these 105 mm and 155 mm systems can still be seen in modern field artillery inventories. Specifically, experience with the M7 and M41 howitzer motor carriages led to the early 1960s development of a military fire support doctrine that still continues to guide U.S. military forces on the modern mobile battlefield. One early conclusion of the doctrinal design work was recognition of the need for a mobile direct-support cannon artillery system that could maneuver on a highly fluid battlefield while providing some level of ballistic protection to the howitzer crew. This conclusion led to the development of two howitzer systems on the same chassis, the M108 and M109.

The M108 105 mm howitzer was originally envisioned for use in the artillery “direct support” role. However, the 12,000-meter maximum range provided by its 105 mm cannon, combined with the limited effectiveness of 105 mm ammunition, were later judged to be inadequate for many of the combat scenarios emerging in the decade following the Korean War. Consequently, attention shifted to the second new U.S. self-propelled cannon system as a candidate to fill the direct-support role.

Firepower on the M109 was provided by a 155 mm cannon with a range of 14,600 meters. The greater forces generated by the increased firepower mandated the addition of two stabilizing spades at the rear of the vehicle to hold the system steady during high charge/low angle and reverse slope fire missions. The range increase may have been relatively minor, but the lethality improvement was significant.

Over the ensuing three decades, the M109 series howitzer would be upgraded and improved through multiple configurations, with remanufactured M109A6 Paladin howitzers still re-entering U.S. Army field artillery inventories in 1999. The M109A6 Paladin Integrated Management program will upgrade Paladins so that they will serve well into the 21st century. Paladins serve in the arsenals of more than a dozen military forces around the world.