Its unique propulsion system which relied solely on compressed air without an explosive propellant rendered it a silent weapon ideal for stealth operations although it could not fire munitions more powerful than darts. Functionally, it was an advanced blowpipe which did not require input of air pressure by its user. In the course of its lifetime, Shay also came to complement it with a grenade launcher.
In contrast to common firearms which used a propellant charge, the air rifle fired projectiles by means of compressed air. While this method of propulsion rendered it incapable of firing higher caliber munitions like bullets, it could be outfitted with darts coated with poison or sedatives. The unique propulsion system also ensured that it made virtually no noise upon firing. As such, it was effectively a technologically upgraded form of the blowpipe favored by the West Indies Brotherhood of the Assassins in the early 18th century and proved quite useful for Shay in stealth operations
In July 1752, the air rifle was en route to Mount Vernon, Virginia as a secret package for the high-ranking Templar Lawrence Washington. It had been picked up by Washington's majordomo and loaded onto a frigate bound for the plantation, a movement detected by agents under Colonial Assassin Hope Jensen. The Assassins responded by sending Liam O'Brien and Shay Cormac, then one of their own, on a mission to tail the frigate to its destination where they could find Washington, assassinate him, and recover the Voynich manuscript in his hands. Uncovering the contents of the package and retrieving it was a secondary objective.
When Shay caught up with the docked frigate at Mount Vernon, the air rifle had not yet been unloaded. Shay, in retrieving the air rifle, accidentally fired a sleep dart at a guard when he was startled by him. Impressed by the silence of the weapon, he thereupon decided to keep it as his own, quickly making effective use of it in driving four guards berserk as he infiltrated the plantation's party. After assassinating Washington, he was allowed to retain the air rifle, and he would from then on carry it with him across all his missions for the Assassins and then the Templars, serving as his signature weapon.
In 1756, Shay outfitted the rifle with the prototype grenade launcher developed by Benjamin Franklin. The inventor had been crafting it for the Assassins but handed it to Shay after being unaware of his defection to the Templars.
- In the cinematic trailer for Assassin's Creed: Rogue, the air rifle is depicted as a regular firearm for dramatic effect. When Shay fires it, a loud explosive sound is heard, contradicting its nature as a silent weapon.
- In the same trailer, Shay wears the rifle on his back with the butt above his shoulder, a more standard and realistic way of carrying it, but in the actual game, he wears it with the barrel above his shoulder.