Obstacles to troop movement

Natural obstacles are represented by those terrain features that for which few troops and their vehicles have capability to traverse. They include water obstacles, or areas of poor drainage such as lakes, rivers, swamps and marshes. The former two can be crossed by amphibious vehicles capable of swimming, or vehicles capable of deep wading after preparation, or by constructing a water crossing, and thus creating an easily targeted choke point. Soil and rock can also represent mobility obstacles if the soil is too soft and unable to support the weight of the military vehicles, or the terrain is fractured by cliffs, or large boulders that make organised movement impossible. While soft soil is relative to vehicle ground pressure, there is little that can be done to negotiate very rocky terrain or cliffs except by using specially trained light infantry troops. Vegetation such as jungles or dense forests can also represent obstacles to movement, in some cases even to light infantry troops. Some natural obstacles can be a result of climatic or soil activity such as deep snow that by covering all terrain makes safe traversing difficult and slow, or landslides that may create an obstruction suddenly despite previously clear route reconnaissance report.

While human habitat had, since early construction of roads, sought to create ways of negotiating terrain faster, the human activity on the landscape can create obstacles in its own right. Artificial lakes and ponds, canals, and areas of agricultural cultivation, particularly those that are water-intensive such as rice-paddy fields create obstacles often more difficult than the natural equivalents. Mining activity creates quarries, and the building of roads, rail roads and dams also involve construction of cuts and fills. Seeded tree-line windbreaks, hedgerows, stone walls and plantation forests also disrupt mobility, particularly of vehicles. Lastly the urban areas in themselves represent obstacles by offering elevated firing positions and canyon-like choke points by forcing the opponent to advance through the streets.

Obstacle for train movement, reinforced concrete.

Constructed obstacles are those prepared by military engineering troops, often combat engineers, by either using materials to construct impediments to foot and vehicle-borne troops, or by using demolition methods, or excavation such as an abatis, to create obstacles from natural materials and terrain in specific location in accordance with the overall plan of operations. Sometimes such obstacles can be created intentionally or unintentionally through effects of artillery fire cratering. Buildings demolished due to combat or aerial bombing become very effective obstacles as rubble represents difficult to negotiate and irregular piles of building materials.

Concealed obstacles are used with the intention of not only preventing movement of enemy troops, but also causing casualties during attempted movement. Although one of the oldest forms of obstacle use, this became far deadlier with the invention of the mine warfare, and more so with air-delivered scattered submunition minelets that can create an instant minefield.

Obstructive obstacles are used primarily to deny terrain visibility to the enemy, thus creating uncertainty in targeting friendly troops. Although ancient in use as tar smoke pots, modern smoke screens are temporary and are used as a tactical measure during manoeuvring, often when a unit is performing a position change.

• Liddell Hart, Basil Henry, The Tanks: The history of the Royal Tank Regiment and its predecessors, Heavy Branch, Machine-Gun Corps, Tank Corps, and Royal Tank Corps, 1914-1945, Cassell, London, 1959