In NATO and most other western countries, motorised infantry is infantry which is transported by trucks or other motor vehicles. It is distinguished from mechanized infantry, which is carried in armoured personnel carriers, infantry combat vehicles, or infantry fighting vehicles. In Russia and the former Soviet Union the term motostrelki (Мотострелки in Russian) is used to indicate mechanized infantry, and during the Korean War this usage prevailed in all Warsaw Pact countries.
Motorising infantry is the first stage towards the mechanisation of an army. Civilian trucks are readily adaptable to military uses of transporting soldiers, towing guns, and carrying equipment and supplies. This greatly increases the strategic mobility of infantry units, which would otherwise rely on marches or railroads. In practice, armies have found it advantageous to develop trucks to military specifications, such as all-wheel drive, in order to have vehicles that function reliably in extremes of weather and terrain.
Motorisation provides no direct tactical advantage in small unit combat, because trucks and jeeps are vulnerable to artillery and small arms fire. However in larger battles motorized infantry have an advantage in mobility allowing them to move to critical sectors of the battlefield faster, allowing better response to enemy movements, as well as the ability to outmaneuver the enemy.
The disadvantage of motorisation is that the formation required many vehicles and supplies of fuel to be of advantage..
The British created the Experimental Mechanized Force between the wars to test the capabilities of all-arms formations of mechanised units, this included motorised infantry.
The speed advantages of motorised infantry first became important in World War II in the German Blitzkrieg. While no more robust than regular infantry moving on foot, its increased speed became decisive in the Blitzkrieg strategy because it could follow the panzer forces and defend its flanks. Notwithstanding the obvious advantages of motorisation, most countries opted only for partial motorisation of their infantry because of the cost and logistical implications caused by the deployment of so many vehicles. Even large armies were affected by these factors. The bulk of German and Soviet infantry remained on foot, while U.S. infantry divisions could, if needed, redirect the activities of enough trucks to motorise an infantry regiment. Likewise, infantry divisions of the UK Britain and its Empire could motorise chosen subordinate units, but infantry advanced on foot in most cases.
Currently in the post Cold War world, motorisation of infantry is becoming more popular since humanitarian deployments are more prevalent with troops acting as quasi-police units. There is also a trend for motorised infantry to be up-armoured due to the situation of insurgency and terrorism in post-invasion Iraq.