Mechanized infantry

U.S. M3 half-tracks and infantry on exercises, Fort Knox, June 1942

As World War II progressed, most major armies integrated tanks or assault guns with mechanized infantry, as well as other supporting arms, such as artillery and engineers, as combined arms units.

Allied armored formations included a mechanized infantry element for combined arms teamwork. For example, US armored divisions had a balance of three battalions each of tanks, armored infantry, and self-propelled artillery. The US armored infantry was fully equipped with M2 and M3 halftracks. In the British and Commonwealth armies, "Type A armoured brigades," intended for independent operations or to form part of armored divisions, had a "motor infantry" battalion mounted in Universal Carriers or later in lend-lease halftracks. "Type B" brigades lacked a motor infantry component and were subordinated to infantry formations.

The Canadian Army and, subsequently the British Army, used expedients such as the Kangaroo APC, usually for specific operations rather than to create permanent mechanized infantry formations. The first such operation was Operation Totalize in the Battle of Normandy, which failed to achieve its ultimate objectives but showed that mechanized infantry could incur far fewer casualties than dismounted troops in set-piece operations.[3]

The German Army, having introduced mechanized infantry in its Panzer divisions, later named them Panzergrenadier units. In the middle of the war, it created entire mechanized infantry divisions and named Panzergrenadier divisions.

Because the German economy could not produce adequate numbers of its half-track APC, barely a quarter or a third of the infantry in Panzer or Panzergrenadier divisions were mechanized, except in a few favored formations. The rest were moved by truck. However, most German reconnaissance units in such formations were also primarily mechanized infantry and could undertake infantry missions when it was needed. The Allies generally used jeeps, armored cars, or light tanks for reconnaissance.

The Red Army began the war while still in the process of reorganizing its armored and mechanized formations, most of which were destroyed during the first months of the German Invasion of the Soviet Union. About a year later, the Soviets recreated division-sized mechanized infantry units, termed mechanized corps, usually with one tank brigade and three mechanized infantry brigades, with motorized supporting arms. They were generally used in the exploitation phase of offensives, as part of the prewar Soviet concept of deep operations.

The Soviet Army also created several cavalry mechanized groups in which tanks, mechanized infantry and horsed cavalry were mixed. They were also used in the exploitation and pursuit phases of offensives. Red Army mechanized infantry were generally carried on tanks or trucks, with only a few dedicated lend-lease half-track APCs.

The New Zealand Army ultimately fielded a division of a roughly similar composition to a Soviet mechanized corps, which fought in the Italian Campaign, but it had little scope for mobile operations until near the end of the war.

The Romanian Army fielded a mixed assortment of vehicles. These amounted to 126 French-designed Renault UE Chenillettes which were licence-built locally, 34 captured and refurbished Soviet armored tractors, 27 German-made armored half-tracks of the Sd.Kfz. 250 and Sd.Kfz. 251 types, over 200 Czechoslovak Tatra, Praga and Skoda trucks (the Tatra trucks were a model which was specifically built for the Romanian Army) as well as 300 German Horch 901 4x4 field cars.[4] Sd.Kfz. 8 and Sd.Kfz. 9 half-tracks were also acquired,[5] as well as nine vehicles of the Sd.Kfz. 10 type and 100 RSO/01 fully tracked tractors.[6] The Romanians also produced five prototypes of an indigenous artillery tractor.

Swiss Armed Forces Panzer 61 and SPz 63/73 armored vehicles deploying mounted infantry in 1979

On July 9, 1945, Decree of the State Defence Committee No. GKO-9488ss, “On the Resupply of Armored and Mechanized Forces of the Red Army”[7] was issued. It ordered the creation of mechanised divisions from many rifle divisions, included in the Armored and Mechanised Troops. In some cases, cavalry divisions and airborne divisions also became mechanised divisions[8] The Soviet motorised rifle troops officially appeared in accordance with the Directive of the Minister of Defense of the USSR No. org. / 3/62540 of February 27 1957. This directive ordered part of the mechanized divisions and all rifle units and formations reorganized into 'motorised rifle' in the period 1957 to 1964.[9] Creation of the motorised rifle troops was facilitated by large-scale mechanisation of the whole Soviet Ground Forces.

This became possible due to the increase in the production of armored personnel carriers, self-propelled guns and so on. For example, in the period before the formation and in the initial period of the formation of the motorized rifle troops:

• BTR-40 - in the period from 1950 to 1960s, 8,500 units were produced[10]
• BTR-50 — 1954 to 1970s — 6,500 pieces[11]
• BTR-152 — 1947 to 1962s — 12,421 pieces
• BRDM-1 — 1957 to 1966s — 10,000 units

One or two motorised rifle regiments were also present in each tank division, and many tank regiments included one motorised rifle battalion.[12]

After 1945, the Soviet Armed Forces and NATO further developed the equipment and doctrine for mechanized infantry. With the exception of airborne formations, the Red Army mechanized all its infantry formations. Initially, wheeled APCs, like the BTR-152, were used, some of which lacked overhead protection and were therefore vulnerable to artillery fire. It still gave the Soviet Army greater strategic flexibility because of the large land area and the long borders of the Soviet Union and its allies in the Warsaw Pact. Armored vehicles meant infantry were capable of overcoming water barriers and having means of protection against Weapons of Mass Destruction.

The US Army established the basic configuration of the tracked APC with the M75 and M59 before it adopted the lighter M113, which could be carried by Lockheed C-130 Hercules and other transport aircraft. The vehicle gave infantry the same mobility as tanks but with much less effective armor protection (it still had nuclear, biological, and chemical protection).

In the Vietnam War, the M113 was often fitted with extra armament and used as an ad hoc infantry fighting vehicle. Early operations by the Army of the Republic of Vietnam using the vehicle showed that troops were far more effective while they were mounted in the vehicles than when they dismounted. American doctrine subsequently emphasized mounted tactics. The Americans ultimately deployed a mechanized brigade and ten mechanized battalions to Vietnam.

The motorized rifle troops of the Soviet Armed Forces were the world's first infantry units that adopted a new class of combat vehicles in 1966 - Infantry fighting vehicles. BMP-1 began entering service in 1966. In the Federal Republic of Germany, an approximate analogue, the Marder, appeared only in 1970. Unlike the APC, which was intended merely to transport the infantry from place to place under armor, the IFV had heavy firepower that could support infantry. The Infantry fighting vehicle concept was subsequently copied by almost all countries of the world.[13][14]

The introduction of the BMP-1 prompted the development of similar vehicles in Western armies, such as the West German Marder and American M2 Bradley. Many IFVs were also equipped with firing ports from which their infantry could fire their weapons from inside, but they were generally not successful and have been dropped from modern IFVs.

Soviet organization led to different tactics between the "light" and the "heavy" varieties of mechanized infantry. In the Soviet Army, a first-line "motor rifle" division from the 1970s onward usually had two regiments equipped with wheeled BTR-60 APCs and one with the tracked BMP-1 IFV. The "light" regiments were intended to make dismounted attacks on the division's flanks, while the BMP-equipped "heavy" regiment remained mounted and supported the division's tank regiment on the main axis of advance. Both types of infantry regiment still were officially titled "motor rifle" units.[15]

A line of development in the Soviet Armed Forces from the 1980s was the provision of specialized IFVs for use by the Russian Airborne Troops. The first of them was the BMD-1, which had the same firepower as the BMP-1 but could be carried in or even parachuted from the standard Soviet transport aircraft. That made airborne formations into mechanized infantry at the cost of reducing their "bayonet" strength, as the BMD could carry only three or at most four paratroopers in addition to its three-man crew. They were used in that role in the Soviet invasion of Afghanistan in 1979.