Walther supply the AGSS and AGNS with most of their pistol weaponary. The most widely used model at the moment is the Walther P99. This is very popular among the agents for its reliability, quick reload, and accuracy.
A recent event involving Walthers in the agency was when Sgt 1st Class Conor "Keano" Keenan was on foot patrol on the grounds, when a man pulled a Walther from his pocket, and started blindly firing. Sgt Keenan was able to disarm the man with no casualties, and it turned out that it was his Walther, which had been earlier stolen. This is what got him promoted to Sgt 1st Class.