What type of ammunition does the CIWS use?

The CIWS, or Close-In Weapon System, is designed primarily for defense against incoming missiles and aircraft. It typically uses 20mm tungsten rounds, which are highly effective for this purpose. The choice of tungsten for these rounds is significant as it provides superior penetration capabilities compared to other materials, which is crucial when engaging fast-moving aerial threats.

The high rate of fire and the specific caliber of 20mm enhance the CIWS's ability to track and destroy threats in a short amount of time, making it a vital component of modern naval air defense systems. The other types of ammunition listed, such as armor-piercing rounds or high-explosive rounds, do not align with the standard armament used in the CIWS, thus reinforcing the appropriateness of the selected answer.