The Armamentarium is an exotic titan chest armor. It can be possibly obtained through random drops, or during some weekends, purchased from Xur for 13 Strange Coin.

How do I get armamentarium?

Sources. Armamentarium can be obtained from loot drops from PVE and PVP, as a Powerful Gear Reward from Nightfalls, Flashpoints, etc. Armamentarium can also be obtained from Exotic Engrams.

What does Armamentarium do?

The Armamentarium is an exotic Titan chest armor first seen in Destiny. It returns in Destiny 2 for the Warmind Expansion, where it grants the wearer an additional grenade charge; this bonus charge does not stack with additional charges from subclass trees.