Rolled homogeneous armour

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Rolled homogeneous armour, or RHA, is a theoretical basic type of steel plate, used as a baseline to compare the effectiveness of military vehicle armour.

Through the end of World War II, the type of armour for almost all tanks and other armoured vehicles was sheets of steel. Increasing the protection on a vehicle meant adding thicker sheets of steel, increasing the vehicle's weight and reducing its mobility. Since then, other forms of armour, incorporating empty spaces and materials such as ceramics or depleted uranium in addition to steel, have been developed. Made ineffective by modern weapons using high-impact or high-temperature cutting jets, RHA itself is obsolete due to advances in vehicle armor.

The more recent term RHAe (Rolled Homogeneous Armour equivalency) is used when giving a rough estimate of either the penetrative capability of a projectile or the protective capability of a type of armour which may or may not be steel.

Because of variations in armor shape, quality, material, and case-by-case performance, the usefulness of RHAe in comparing different armour is debatable.

[edit] Specifications

For current United States Army use, RHA steel is produced to Military standard MIL-A 12560 by several manufacturers. The newest standard used is MIL-A-46100. ^[1] It is very similar to but not identical to standard high strength steel alloy 4340 in the AISI steel grades, though mechanical properties are very similar to that alloy. ^[2]