Titanium-A armor

Titanium-A Armor is the most common battle plating used by the UNSC. It is composed of a high-grade Titanium-50 alloy that is usually brownish in color. This cannot be pure titanium because titanium is the only known metal while in pure form that burns with nitrogen-rich atmosphere. Titanium-A has numerous uses throughout the UNSC. This is due largely to titanium's properties; it is light and extremely strong; with a high tolerance for heat. It took newfound importance after the beginning of the Human-Covenant War. To contend with the Covenant's plasma weaponry, humans needed armor that would withstand the heat. This however, is usually boiled away in seconds and does not effectively dissipate the plasma either.

Its primary use is as armor for ships. UNSC Frigates have sixty centimeters of plating on their hull, and UNSC Destroyers have up to two meters of it. The Trafalgar had 10 meters. Marines sometimes have thin Titanium-A armor suits, though these are an increasingly rare sight. These suits are slowly being replaced by ceramic variants, such as those seen on the ODSTs in Halo 3.

The UNSC uses Titanium-A for construction of bases as well, to make them less susceptible to destruction. Places such as HIGHCOM Facility Bravo-6, CASTLE Base and Camp Hathcock used Titanium-A armor in their superstructures.