glacis

A glacis (pronounced /ˈɡleɪsɪs/, French: [ɡlasi]) in military engineering is an artificial slope of earth used in late European fortresses so constructed as to keep any potential assailant under the fire of the defenders until the last possible moment. On natural, level ground, troops attacking any high work have a degree of shelter from its fire when close up to it; the glacis consists of a slope with a low grade inclined towards the top of the wall. This gave defenders a direct line of sight into the assaulting force, allowing them to efficiently sweep the field with fire from the parapet.

The attackers are further frustrated by a deep ditch situated between the glacis and the wall itself, bounded on either side by the smooth, masoned scarp and counterscarp.

Diagram Showing Glacis

More generally, the term glacis can denote any slope, natural or artificial, which fulfils the above requirements. The etymology of this French word suggests a slope made dangerous with ice, hence the relationship with glacier.

Armored vehicles

The term glacis plate describes the sloped front-most section of the hull of a tank or other armored fighting vehicle.^[1] In a head-on-head armored engagement, the glacis plate is the largest and most obvious target available to an enemy gunner. Anti-tank mines which employ a tilt-rod mechanism are also designed to detonate directly underneath the glacis plate. As a result, the glacis plate is generally the thickest, most robust armored section of a tank, followed by the turret face and mantlet.

US M1A1 Abrams main battle tank, edited to identify features (glacis plate highlighted in green)

Geology

An erosional or depositional pediment, with little slope. Erosional glacis occur mostly in arid regions, and result from intense meteorization (weathering) and surface transport via laminar, episodic water flow.

See also

• Fortification
• Siege
• Sloped armour

References

1. ^ Encarta Online Dictionary: Glacis plate, retrieved on 14 December 2008. Archived 2009-10-31.