Improvised vehicle armour is a form of vehicle armour consisting of protective materials added to a vehicle such as a car, truck, or tank in an irregular and extemporized fashion using available materials. Typically, improvised armour is added in the field and it was not originally part of the design, an official up-armour kit, nor centrally planned and distributed. Improvised armour is used to protect occupants from small arms, crew-served weapons, artillery (or tank gun) fire, and mines. Improvised additions have included metal plate, scrap metal, sandbags, concrete, wood, and, since at least the 2000s, Kevlar. These materials vary widely in their ballistic protection.
Improvised vehicle armour has appeared on the battlefield for as long as vehicles have been used in combat. Though usually used in military or conflict contexts, improvised vehicle armour has also been used in non-combat contexts, such as to protect the vehicles of strikebreakers.
World War I
The first armoured cars to see combat in World War I were entirely improvised, although this soon changed as the war continued. A few were used by the Belgian Army during the German invasion. The British Royal Naval Air Service received reports of this and converted some of their own cars. Improvised conversion continued until December 1914 when the first standardized design entered service. The British Royal Naval Air Service in Dunkirk sent teams in cars to find and rescue downed reconnaissance pilots in the battle areas. They mounted machine guns on them and as these excursions became increasingly dangerous, they improvised boiler plate armouring on the vehicles using metal provided by a local shipbuilder.
World War II
Most armies involved in World War II adopted some form of improvised armour at some point. The Home Guard in the United Kingdom equipped itself with a number of vehicles with improvised armour, such as the Bison concrete armoured lorry, intended to be used for defending airfields. Later in 1944, some Cromwell and Churchill tanks had sections of tracks attached to their existing armour to provide yet more extra protection. US M8 Greyhound armoured car crews would sometimes line the floors of their vehicles with sandbags to provide extra protection against landmines.
The addition of improvised armour to tanks was performed by both Axis and Allies forces due to the arms race between the designers of antitank weapons and the designers of tank armour. In some cases, a tank that was effectively protected against existing antitank weapons at the time of its manufacture ended up, once finally tested and delivered to the battlefield, being vulnerable to newly designed antitank weapons. As such, tank crews would ask field repair workshops to increase their protection, using a wide range of armouring principles, including welded or bolted on metal "skirts" around treads and turrets (spaced armour) and welded screens (slat armour). Some German improvised armour was designed to protect weak points, such as sandbags added by Afrika Korps tank crews to the turret joint. On the Eastern Front, some tank crews added sandbags due to fears of magnetic mines.
The German military became aware of these improvised armour approaches used by their troops and issued a recommendation against using most of them in 1944 in the Nachrichtenblatt der Panzertruppen (Newsletter for the Armoured Forces). While the German military was aware that improvised armour boosted tank crews' morale (by giving a sense of increased security) the analysts argued that many improvised armouring techniques were not effective. For example, welding spare tank treads to a turret was not effective, as treads were not armour-grade steel, and concrete was found to offer little protection while also leading to excess fragmentation. Some improvised armour, such as adding concrete or welding on tank treads on an 80 to 90-degree angle, actually made enemy weapons more effective, and both approaches overtaxed the tanks' powertrains from the extra weight.
Welding on improvised Schürzen (skirting) was not permitted, due to concerns that welding the original factory plate armour could weaken it; however, using brackets to mount turret-side and back skirts or side skirts was permitted. Side skirts were permitted because the Soviet 14,5 mm antitank rifles could penetrate the less-armoured sides of the Panzer.