Titanium-A armor

Titanium-A armor is the most common form of battle plating used by the UNSC on its warships. It is composed of high-grade Titanium-50 that is specially strengthened at the molecular level, which implies alloying with other elements. It 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 a new found 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 of the directed plasma. Despite its strength and resistance to heat, however, the Titanium-A plating is usually boiled away within seconds, and does not effectively dissipate the plasma.

Its primary use is armor for ships. UNSC frigates have sixty centimeters of plating on their hull, and UNSC destroyers have up to two meters of plating. UNSC supercarriers like the had 10 meters. Marines sometimes wear thin Titanium-A armor suits. Later in the war, these suits were replaced by ceramic armor suits, such as those used by the Orbital Drop Shock Troopers.

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.

Titanium-A3 Armor
Titanium-A3 armor is a variant of Titanium-A battle plating. Like Titanium-A, it is scientifically altered for stronger hulls of ships, but in tune with a more advanced molecular design than the armor's earlier variant. It's use has only been noted to that of the UNSC Infinity. This armor likely existed good into midst of the war, upon the construction of the Infinity starting in 2537. One can assume that this armor is much stronger than its original by looking at the hulls of ships: the Trafalgar had 10m of Titanium-A armor; and the Infinity had 4.9m of Titanium A-3 armor. The Infinity is the largest and most advanced ship created by the UNSC, with this in mind, it is highly unlikely the Trafalgar would be given a hull twice as strong.