Titanium-A armor is the most common and typical battle plating used by the UNSC on ships. It is composed of a high-grade Titanium-50 alloy, specially strengthened at the molecular level, that is usually greyish in color. Titanium-A has numerous uses throughout the UNSC due largely to titanium being lightweight and extremely strong, with a high tolerance to heat. It took on new found importance after the beginning of the Human-Covenant war to contend with the Covenant's plasma weaponry, Humans needed armor that could withstand the heat of directed plasma. Despite its strength and resistance to heat, the Titanium-A plating is usually boiled away within seconds, and does not effectively dissipate the plasma.
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 plating. Supercarriers like the UNSC Trafalgar had 10 meters. The UNSC Infinity has a mere 4.9 meters, but it is composed of the artificially strengthened Ti-A3 and is protected by Forerunner shielding. Marines sometimes have thin Titanium-A armor suits, though these suits are an increasingly rare sight since they 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.