A2 scope

Are you looking for A2, a Voi water facility?

"Huh... my ass! Well, you can forget about those adjustments to your A2 Scope..."

— A Master Gunnery Sergeant to Johnson, before being cut off by the elevator.

Not much is known about the A2 Scope, but that it was most likely a scoped weapon attachment and was mentioned by "Master Gunns" during The Armory Level on Halo 2. "Master Guns" had said that Avery Johnson would not be receiving adjustments to said device after he inquired on how Johnson had survived the detonation of Alpha Halo, and the Sergeant Major responded by saying it was classified.

It is safe to assume that the A2 scope may be on either the sniper rifle or battle rifle, as Johnson is seen with both quite often. The A2 scope would be probably referring to the BR55 Rifle, since A2 probably means 2x animated scope. This scope may be only a 2x zoom, as it's rarely referred to on the S2 AM Sniper Rifle.