Infantry, Part I: Regular Army /The Pentomic Concept and CARS

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CMH 60-3: Infantry, Part I: Regular Army
John K. Mahon and Romana Danysh
The Pentomic Concept and the Combat Arms Regimental System
U.S. Army Center for Military History publication
  • The Pentomic Concept and the Combat Arms Regimental System

  • The armistice in Korea did not bring about the rapid demobilization of infantry units that traditionally followed the cessation of hostilities in American military history. President Dwight D. Eisenhower gave the reason for this departure from the usual pattern when he said: "We have won an armistice on a single battleground-not peace in the world. We may not now relax our guard nor cease our quest." There was, nevertheless, a gradual reduction of both personnel and units throughout the mid-1950's. When the Korean armistice was signed, the active Army had ninety infantry regiments, a year later the total was seventy-four, and by the end of 1956 only fifty-four regiments were active. The number of separate infantry battalions decreased from thirty-one to twenty-six during the same period, while the infantry's personnel strength dropped from 251,685 to 133,931.
  • By December 1954, all National Guard infantry units that had been federalized during the Korean War reverted to state control and were reorganized at their home stations. Several Regular Army infantry regiments were activated to replace them in the active Army. The number of these organizations, however, never equaled the total of National Guard units released, and some of the Regular regiments were inactivated as the authorized strength of the Army declined. Although the number of units decreased, the responsibilities of the infantry remained worldwide. In December 1956, in addition to those in the continental United States, infantry units were stationed in the Canal Zone, Alaska, Hawaii, Iceland, Italy, Berlin, West Germany, Japan, and Korea. In Korea, two infantry divisions with three organic infantry regiments each were still on duty.
  • The period immediately following the Korean War was a difficult time for the infantry. The new administration re-evaluated the national military policy, and with this "New Look" the United States entered the so-called "Era of Massive Retaliation." The doctrine of massive retaliation rested on the assumption that the threat of instant and large-scale nuclear reprisals would serve as an effective deterrent to future wars and, therefore, make large conventional forces unnecessary. It emphasized the role of the Air Force in national defense and relegated the Army with its infantry to an inferior position.
  • Unable to convince the administration of the likelihood of small limited wars in the future and of the need for what he called "a strategy of flexible response," General Maxwell D. Taylor (then Army Chief of Staff) decided that it was necessary to reorganize and modernize the Army to make it readily adaptable to the requirements of the atomic battlefield. As a result, starting in late 1956 Army units were reorganized under the Pentomic system. Two of the most salient characteristics of this concept were reflected in its name-pentagonal structure and atomic capability. Low-yield tactical nuclear weapons became a mainstay of the Army, and an organization based on five major subordinate units replaced the traditional three basic elements of the triangular system.
  • Many features of the Pentomic organization were dictated by the nature of atomic warfare as well as by a desire to take full advantage of the tremendous technological advances of recent years. For example, the absolute requirement for wide dispersion on the nuclear battlefield to avoid offering the enemy any single lucrative target was an important consideration in adopting an organization with five small basic combat units, while new developments in the field of communications made a broader span of control possible. Since the Soviet Union had acquired an atomic capability in 1949 and from all indications its nuclear arsenal had kept on growing steadily, an enemy with atomic combat power was not entirely theoretical. In order to be successful in a nuclear war, U.S. infantry units had to be small and lean, more powerful and harder hitting, self-sufficient, and geared for long periods of independent action on a wide and fluid battlefield. They had to be capable of rapid and effective concentration in the attack as well as equally rapid dispersal for defense. The Pentomic system attempted to give the infantry all of these capabilities.
  • The reorganization went through several stages. The Continental Army Command (CONARC), which replaced the Office, Chief of Army Field Forces, on 1 February 1955, began studies of the new concept in the fall of 1955. Test TOE's entitled "Reorganization of the Airborne Division (ROTAD)," "Reorganization of the Current Armored Division (ROCAD)," and "Reorganization of the Current Infantry Division (ROCID) " were published on 10 August, 1 December, and 20 December 1956, respectively. By June 1958, all fifteen active Regular Army divisions and their subordinate units had been reorganized under these tables, and by mid-1959 all but one of the thirty-seven divisions in the reserve components had adopted the new structure. Meanwhile the system was being field tested and evaluated by CONARC, and the Infantry School was revising infantry manuals to cover Pentomic organization and warfare on the nuclear battlefield. In December 1958, a major Infantry Conference, the first such gathering since 1946, met at Fort Benning, Georgia, to discuss the radical changes that were taking place in infantry organization, materiel, and tactics. The ROTAD tables were superseded by the final TOE's for Pentomic airborne units on 31 June 1958, but the final D-series tables for elements of infantry and armored divisions were not published until 1 February and 1 May 1960.
  • Pentomic was basically a divisional reorganization and as such is beyond the scope of this narrative, but it did introduce major changes in all infantry units. The single most important innovation was the elimination of the regiment from the infantry structure. It was replaced by a new organization called the "battle group." Smaller than a regiment and larger than a battalion, the new unit was commanded by a full colonel. Five battle groups were organic to the Pentomic infantry division.
  • The strength of the ROCID battle group was 1,427, but this was reduced to 1,356 by the D-series TOE. Initially it consisted of a headquarters, headquarters and service company; an artillery battery, equipped with 4.2-inch mortars; and four rifle companies, each having four rifle platoons and a weapons platoon. After reorganization under the D-tables, the battle group had a headquarters and headquarters company, a combat support company, and five rifle companies composed of three rifle platoons and a weapons platoon. All of the tactical support elements (including a radar section and reconnaissance, heavy mortar, and assault weapons platoons) were located in the combat support company. The radar section's two medium-range and five short-range radar sets greatly increased the battle group's ground surveillance capability, while the heavy mortar platoon brought the 4.2-inch mortar back to the infantry. The assault weapons platoon introduced the first operational infantry guided missile, the French-manufactured SS10, a lightweight, long-range, and accurate weapon, employed primarily against tanks.
  • The weapons platoon in the Pentomic rifle company became a much more powerful unit since it no longer used 60-mm. mortars and 57-mm. recoilless rifles. It now had 81-mm. mortars and 106-mm. recoilless rifles, which prior to ROCID were classified as battalion-level equipment. The 106-mm. rifle had been adopted in October 1954 as a replacement for the 75-mm. and 105-mm. recoilless rifles in the infantry battalion's heavy weapons company. This was the only significant change in infantry weapons between the Korean armistice and the Pentomic reorganization. The ROCID and I)-series TOE's made the 106mm. recoilless rifle a standard rifle company weapon, giving the unit highly effective antitank protection.
  • The tank company organic to the pre-ROCID infantry regiment was not continued in the Pentomic structure. The divisional tank battalion, however, was reorganized to consist of five tank companies, so that a company of seventeen tanks was available to support each of the five battle groups. Other divisional elements, normally providing direct support for battle groups, were also organized pentagonally.
  • The Pentomic infantry rifle squad had eleven men, two more than the squad of the Korean War era. This increase represented more than just a gain of two additional rifles. It introduced the concept of two fire teams within a squad and gave the unit not only increased firepower, but also greater maneuverability, the ability to withstand more attrition, a greater capacity for sustained combat, and more effective control over individual riflemen. Under the 1960 TOE, a portable radio set was issued to each of the three rifle squads and to the weapons squad. These radios were part of a newly established platoon net linking together, for the first time, all subordinate elements of the rifle platoon and making them immediately responsive to the platoon leader's orders. Communications were improved on other organizational levels as well, because a rapid and efficient communications system was an essential ingredient of the Pentomic concept.
  • Since a high degree of mobility was another requirement of Pentomic units, transportation equipment was also improved. In addition to employing its own organic transport, the battle group could depend on the divisional transportation battalion, which was added to the structure under ROCID. This unit's two armored personnel carrier companies were capable of moving an entire infantry battle group. By also using its light truck company, the transportation battalion could move two battle groups simultaneously. As for organic aviation, the battle group did not inherit the regiment's 6-man aviation section. All of the aircraft, both rotary and fixed-wing, authorized for the Pentomic infantry division were centralized in one combat aviation company. The company was organized to give direct support to battle groups when needed as well as to furnish general support for the entire division.
  • When organized for combat, the infantry battle group often had other units attached. These were usually a tank company, an engineer company, and a field artillery battalion. A battle group, reinforced in this manner, was a balanced combined arms force and, although considerably smaller, greatly resembled the regimental combat teams of World War II and the Korean War. Most infantry battle groups were divisional units. There were, however, some nondivisional groups which were assigned to higher commands or served as school troops. Others were organic to a new organization, the separate infantry brigade. Two such brigades, the 1st and 2nd, were activated in the Regular Army in 1958. In the Army National Guard, the 29th, 92nd, and 258th Infantry Brigades were organized in 1959 with their respective headquarters in Hawaii, Puerto Rico, and Arizona.
  • The airborne infantry was also reorganized under the Pentomic system. The units organic to the 101st Airborne Division were the first in the Army to be evaluated and tested under the new concept. In September 1956, the 101st was reorganized in accordance with the ROTAD TOE's, and the following month tests of the new structure began at Fort Campbell, Kentucky, and Fort Bragg, North Carolina, in a series of exercises called JUMP LIGHT. The name given to the exercises reflected one of the most important characteristics of ROTAD units-their relative lightness. The entire division, with the personnel and equipment of all of its elements, including five airborne battle groups, was completely transportable by Air Force medium transport aircraft (the C-119, C-123, and C-130) . Some of the equipment provided by the TOE's was not yet available and interim items authorized did not meet all of the airlift criteria, but it was understood that these items were only temporary issue and would be replaced as soon as possible.
  • The airborne battle group was similar to the corresponding unit in the regular infantry. Under ROTAD it contained 1,584 men, organized into a headquarters, headquarters and service company, a heavy mortar battery, and five airborne infantry companies. With the adoption of the D-series TOE, total group strength increased by only one man and its basic structure remained the same. Each of the five rifle companies had four rifle platoons and a weapons platoon, which was equipped with 81-mm. mortars and 106-mm. recoilless rifles. The rifle platoon consisted of a weapons squad and three rifle squads, composed of eleven men and organized into two fire teams. The group's organic fire support was provided by an artillery battery, armed with eight 4.2-inch mortars, while its assault gun platoon was equipped with six 90-mm., selfpropelled, fulltracked antitank guns, which could be transported and landed by C119 or C-123 aircraft or dropped by parachute from the C-119.
  • In recognition of the importance of communications on the modern battlefield, the signal equipment of the airborne battle group was made greatly superior to that of the former airborne infantry regiment. Although the total strength of the battle group was less than half that of the regiment, the group was authorized the same number of radios and even more telephones than had been organic to the regiment. In addition to its 100 percent air transportability, the Pentomic airborne battle group also had increased ground mobility. The most significant development in this field was the adoption of the infantry light weapons carrier, M274, better known as the mule or mechanical mule. By taking some of the load off the paratrooper's back, the mechanical mule improved the mobility of airborne infantry units in ground operations.
  • In comparison with the almost complete transformation of standard and airborne infantry units during the Pentomic era, changes in armored infantry structure during the same period were minor. With the battalion as its basic element, the armored infantry was already organized into small, powerful, flexible, and highly mobile units, capable of the rapid concentration and wide dispersion which would be essential in nuclear warfare. The armored division's combat command organization was also well suited to the atomic battlefield. Therefore, although the armored division gained an atomic capability under the ROCAD and D-series TOE's, it did not adopt the pentagonal structure. The division retained both its three combat commands and its four organic armored infantry battalions. Each battalion continued to have four rifle companies consisting of three rifle platoons and an 81-mm. mortar platoon. The total strength of the battalion, however, increased somewhat from 978 to 1,027, and the unit was designated an armored rifle battalion.
  • Two BAR's had been authorized for each rifle squad in the regular and airborne infantry during 1953 and 1954, but the second automatic rifle was not included in the armored infantry rifle squad until the ROCAD TOE of December 1956. At the same time the squad increased from ten to twelve men and, like its 11-man standard and airborne infantry counterparts, was subdivided into two fire teams. The extra man drove the squad's organic M59 armored personnel carrier (APC), a fulltracked amphibious vehicle with ground mobility equal that of a tank and having great agility in water. Meanwhile, a lighter and less expensive amphibious armored personnel carrier, M 118, was being developed. Although designed primarily to give the armored infantry mobility, the M113 could also be employed as a self-propelled heavy weapons carrier, an ambulance, a command vehicle, a cargo carrier, or a fire direction center. Under the 1960 TOE's, there were seventeen APC's in each armored infantry company and a total of seventy-seven in the armored rifle battalion. The battalion had enough organic transportation to make it 100 percent mobile, and its communications system was more extensive and more efficient than ever before.
  • One very important item, authorized by the D-series TOE's for all types of infantry units, was the new M14 rifle. The result of more than ten years of experimentation arid testing, the M14 was almost a pound lighter than its predecessor, the M 1 rifle, and held a 20-round magazine instead of the Ml's 8round clip. Since it fired the 7.62-mm. cartridge adopted by the other NATO countries, standard U.S. rifle ammunition became interchangeable with that of major allies. A selector for automatic or semi-automatic fire increased the M 14's versatility and enabled it to serve as a replacement not only for the M 1, but also for the carbine, the submachine gun and, when used with a bipod, for the much heavier BAR. Because any rifleman could now become an automatic rifleman with little additional training, the rifle squad and other small infantry units acquired greater tactical flexibility. Although the M1 and the BAR had served the infantry well for many years and most soldiers were sorry to see these "old reliables" go, the M14 was adopted as the new standard weapon of the rifleman and began to be issued to infantry units in 1960. Shortly thereafter, TRAINFIRE, the official rifle marksmanship course since 1957, designed to simulate actual combat conditions and featuring a pop-up silhouette target known as "Punchy Pete," was modified for use with the M-14.
  • At about the same time, a new general purpose machine gun, the M60, was adopted as a replacement for both the heavy water-cooled and the light air-cooled Browning .30-caliber machine guns. The M60 fired 7.62-mm. NATO ammunition at a rate of 600 rounds per minute, weighed only twenty-three pounds, and could be fired from the shoulder or hip, from an attached bipod, or from a newly developed aluminum tripod. Other infantry weapons and equipment were meanwhile being developed and tested by the Infantry School and by CONARC's Infantry Board. Among them were a lightweight rifle, a shoulder-fired air defense guided missile, an improved model of the 81-mm. mortar, a new grenade launcher, more powerful and lighter radar sets, the Claymore antipersonnel mine, and better radios, including an experimental combat helmet model. Thus, although the spectacular advances made during the Pentomic era were in the fields of nuclear weapons, giant guided missiles, and huge rockets, there was also solid progress in the development of conventional small arms and equipment for the individual rifleman.
  • The Pentomic concept brought about the most drastic reorganization of infantry units since triangularization. When the square divisions became triangular, one infantry regiment had to be dropped from each division. Pentomic affected all of the infantry elements organic to the infantry and airborne divisions, leaving only the infantry battalions in the armored division relatively unchanged. Since both regiments and battalions were eliminated in the regular and airborne infantry,. the chain of command went directly from the division headquarters to the five new battle groups and from there to the company level. The combined strength of the three regiments under the last triangular TOE was 10,560 in the infantry division and 10,088 in the airborne division. Under ROCID the five infantry battle groups totaled 7,185 men, while the five ROTAD airborne battle groups had a strength of 7,920. In both cases, therefore, the Pentomic reorganization caused a significant reduction in infantry personnel. By eliminating the traditional regiment, it also raised the question of what the new infantry units were to be called, how they were to be numbered, and what their relationship to former organizations was to be.
  • If some means of perpetuating the history of infantry and other combat regiments had not been combined with the tactical reorganization, hundreds of independent units would have been created with no historical affiliation. The numerical designations of such a multiplicity of separate units would have run into three or possibly four digits. At the same time, the failure to pass regimental lineages and honors to the new Pentomic units would have brought an end to the history and traditions acquired by U.S. Army combat regiments in the past. Such difficulties were avoided by the adoption of the Combat Arms Regimental System (CARS), a plan developed by the Army Staff on the model of the British regimental system and approved by the Secretary of the Army on 24 January 1957. CARS was designed to maintain the continuity of the Army's distinguished combat units and to provide an organizational framework that would remain stable in spite of fluctuations in strength and tactical structure. It also gave every combat soldier the opportunity of being a member of a traditional unit, one of which he could be genuinely proud, thereby improving troop morale and esprit de corps.

Combat Arms Regimental System Infantry Regiment Table of Organization and Equipment

  • The system was built around the regiment for two reasons. First, the regiment had always been the principal repository of unit history and tradition in the United States Army. Second, since it was becoming obsolete as a tactical unit, the regiment would no longer be subject to periodic reorganizations and could serve as a permanent vehicle for perpetuating unit lineage, honors, and customs without restricting future organizational trends. Consequently, a number of distinguished infantry, artillery, armor, and cavalry regiments were selected and designated as so-called parent units. Each infantry parent regiment was capable of providing a base for a variable number of tactical elements, which could be battle groups, battalions, or companies. Their number and size varied according to the needs of the Army, but each element traced its lineage back to one of the organic companies of the parent regiment. When the element was a battle group or battalion, its headquarters was the direct descendant of one of the former regimental companies, while its own organic elements were constituted as new units.
  • Elements of the same parent regiment could be assigned to different divisions or other commands and could be allotted to either the Regular Army or the Army Reserve. These two components shared their CARS regiments, while the Army National Guard had its own, those traditionally associated with a given geographic area. The Regular Army and Army Reserve parent units were selected on the basis of a point system which credited one point per year since original activation and two points for each campaign credit and American decoration. Initially, fifty-five infantry regiments were chosen: the 1st through 23rd, 26th through 32nd, 34th, 35th, 36th, 38th, 39th, 41st, 46th, 47th, 48th, 50th, 51st, 52nd, 54th, 58th, 60th, 87th, 187th, 325th, 327th, and 501st through 506th. Because of their airborne backgrounds, the last nine designations on this list were reserved for airborne units; the 6th, 36th, 41st., 46th, 48th, 50th, 51st, 52nd, 54th, and 58th Infantry became parent regiments for the armored infantry with which they had been associated in the past; the remaining thirty-six were for the regular infantry. The infantry elements of the 1st Cavalry Division were not assigned to infantry parent units but had cavalry parent regiments, which they shared with cavalry reconnaissance units. (Their lineages are included in the Armor-Cavalry volume of the Army Lineage Series.)
  • In 1959 eighteen more infantry regiments, all with Army Reserve backgrounds, were added to the list of parent units, since reservists felt that it was detrimental to the morale of the Army Reserve not to have any parent regiments of its own. The 59th, 305th through 307th, 313th through 315th, 357th through 359th, and 442nd Infantry were chosen because of their outstanding records, and the 100th Battle Group, 442nd Infantry, from Hawaii was permitted to retain the number under which it had distinguished itself during World War II. The seven other infantry regiments selected (the 322nd, 345th, 381st, 383rd, 409th, 410th, and 411th) had special ties with certain communities. They were organized with only one element each, their lineages differing somewhat from those of other CARS units.
  • The reorganization of airborne and standard infantry units under CARS was a relatively simple procedure because they had retained the regimental structure up to that time. The former armored infantry regiments, however, had been broken up into battalions for many years, and it was necessary to restore them to their original regiments. Many battalion designations made famous in World War II combat were lost in the process, but their honors were perpetuated by the new CARS units. Under CARS there were two kinds of honors, earned and shared. All elements of the parent unit shared the regimental campaign credits and decorations. Color bearing units identified their own contributions to the regiment's honors by special devices on campaign and decoration streamers and by asterisks on their official Lineage and Honors Certificates. Company-sized units, which were authorized guidons, displayed only those honors that they themselves had earned. Provisions were also made for recognition of honors awarded subsequent to the adoption of CARS.
  • As originally planned, Phase V of the system had provided for the establishment of a regimental headquarters, not as it had existed prior to CARS, but as a home for all members of the regiment. The headquarters would be assigned to a permanent location and would maintain regimental history and traditions, keep records, display colors, trophies, and other properties, and perhaps conduct regimental recruiting and operate regimental training units. A proposal to centralize all infantry regimental headquarters at the Infantry Center at Fort Benning, Georgia, was tentatively approved by the Army Staff in 1959, but it was rejected the following year because of lack of funds, personnel, and appropriate on-post facilities. As of 31 December 1969, Phase V of CARS had not yet been implemented. Headquarters of former infantry regiments remained at zero strength under Department of the Army control and, pending their establishment, the lowest numbered or lettered active element of each regiment was designated as the custodian of the regimental colors. It was also the unit which usually displayed regimental historical properties and co-ordinated the selection of a regimental unit day. Members of all elements of a CARS parent regiment shared the regiment's distinctive insignia, although they could wear different shoulder sleeve insignia, depending upon the division or other command to which their unit was assigned.
  • In general, redesignation of infantry units to conform to CARS was accomplished simultaneously with their reorganization under the Pentomic concept. Only the elements of the 101st Airborne Division, which became Pentomic in 1956 prior to approval of CARS, had to be reorganized again in April 1957 to include the proper new designations. In June 1956, just before the Pentomic reorganization began, there had been fifty-nine infantry regiments (with three battalions each) and twenty-three separate infantry battalions in the Regular Army. By June 1958 they had been replaced by seventy-six Pentomic battle groups and nineteen armored rifle battalions, all of which were elements of fifty-five infantry and five cavalry CARS parent regiments. CARS and Pentomic were not limited to the Regular Army; all Army National Guard and Army Reserve infantry units were also reorganized according to the new historical and tactical organizational systems. The only exceptions were the training regiments of the thirteen training divisions in the Army Reserve, which were organized under entirely different TOE's and were neither Pentomic nor CARS units.


This work is in the public domain in the United States because it is a work of the United States federal government (see 17 U.S.C. 105).