Helm

A Helm is a piece of armor which covers one's head. Aside from an awesome accesory for a period look, the helm serves a very important purpose:

3.2.2.4. Class 4 (missile) Weapons cause two hits of Injury to a Target Area. A Class 4 Weapon striking an Armored portion of the Head causes no Injury.
3.2.2.5. Class 5 (Head only missile) cause 1 hit of Injury to an unarmored Head area. A Class 5 Weapon striking an Armored portion of the Head area causes no injury.

In other words, if you have a helm, your head is invulnerable to arrows, javelins and rocks, as long as they don't hit you in the face.

See Also:

• Book of War