Mechanized infantry is infantry equipped with armored personnel carriers or infantry fighting vehicles for transport and combat. Mechanized infantry is distinguished from motorized infantry in that its vehicles provide a degree of protection from hostile fire, most APCs and IFVs are fully tracked or are all-wheel drive vehicles, for mobility across rough ground. Some nations distinguish between mechanized and armored infantry, designating troops carried by APCs as mechanized and those in IFVs as armored. The support weapons for mechanized infantry are also provided with motorized transport, compared with light truck-mobile infantry, mechanized infantry can maintain rapid tactical movement and, if mounted in IFVs, has more integral firepower. It requires more combat supplies and ordnance supplies, and a larger proportion of manpower is required to crew. For example, most APCs mount a section of seven or eight infantrymen but have a crew of two, most IFVs carry only six or seven infantry but require a crew of three. To be effective in the field, mechanized units also require many mechanics, with specialized maintenance and recovery vehicles, arguably, the first mechanized infantry were assault teams mounted on A7V tanks. The vehicles were extra-large to let them carry sizeable assault teams, all-machine gun armed A7V tanks carried two small flame throwers for their dismounts to use. A7V tank would often carry a second officer to lead the assault team, during the Battle of St. Quentin, A7Vs were accompanied by 20 stormtroopers from Rohr Assault Battalion, but it is unspecified if they were acting as dismounts or were accompanying the tanks on foot. During the battle, tank crews were reported to dismount and attack enemy positions with grenades, towards the end of World War I, all the armies involved were faced with the problem of maintaining the momentum of an attack. Tanks, artillery, or infiltration tactics could all be used to break through an enemy defense and it was widely acknowledged that cavalry was too vulnerable to be used on most European battlefields, but many armies continued to deploy them. Motorized infantry could maintain rapid movement, but their trucks required either a road network or firm open terrain. They were unable to traverse a battlefield obstructed by craters, barbed wire, tracked or all-wheel drive vehicles were to be the solution. Following the war, development of mechanized forces was largely theoretical for some time, although some proponents of mobile warfare, such as J. F. C. Fuller, advocated building tank fleets, other, such as Heinz Guderian in Germany, as the Germans rearmed in the 1930s, they equipped some infantry units in their new Panzer divisions with the half-track Sd. Kfz. 251, which could keep up with tanks on most terrain, the French Army also created Light Mechanized divisions in which some of the infantry units possessed small tracked carriers. Together with the motorization of the infantry and support units. The German doctrine was to use them to exploit breakthroughs in Blitzkrieg offensives, 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
U.S. Army mechanized infantry dismount from an M113 armored personnel carrier during training in 1985.
21 March 1918: German A7V tanks in Roye, Somme during the 1918 Battle of France.
German SdKfz 251 half-track APC
U.S. M3 halftracks and infantry on exercises, Fort Knox, June 1942