In what condition should the weapon be when returned to the armory?

When returning the M9 service pistol to the armory, it should be in condition four. Condition four refers to the state of the firearm when it is completely unloaded, with the magazine removed and the action open, allowing for a visual inspection of the chamber. This condition is crucial for safety in the armory where multiple weapons may be stored and handled by different personnel. Ensuring that the weapon is unloaded and visually verified minimizes the risk of accidental discharge and promotes a safe environment.

In contrast, the other conditions involve varying degrees of readiness, such as having a round in the chamber or the magazine inserted, which would make the firearm potentially operable and pose unnecessary risks in a storage environment. Hence, condition four is the appropriate choice for securing the weapon safely when it is returned to the armory.