Mauer der Toten: CRBR-S

The Cerberus

The Conversion-Ready Binary Repeater-Standard, CRBR-S, is the Wonder Weapon of Mauer der Toten, the first one Requiem built. In its base form it is an automatic pistol; a floating sphere, the Copy-Cat, turns around it and fires a second shot each time it is fired, at no cost in ammo. An artificial intelligence speaks through it, with the voice of Elizabeth Grey, Oskar Strauss or Mackenzie Carver.

CRBR-S

Automatic, 25 rounds a magazine, with 75 in reserve.

Getting it

The CRBR-S comes from the Mystery Box, the Trials, the golden chest of the Mister Peeks nightclub, or a free quest:

Klaus and the bedroom: rebuild Klaus. The bedroom of Hotel Room 305, opened for his hands, holds a locked safe.
The blacklight: send Klaus to the locker of the Switch Control Room, next to Mule Kick, and take the blacklight.
Three numbers: under the blacklight, a number written in invisible ink appears in each of three places, in this order: the Garment Factory, the Service Passage and the Grocery Store. Each number can be in one of three spots of its room.
The safe: in Hotel Room 305, enter the three numbers on the dials of the safe, from left to right. The zombies ignore the player while they dial. The safe opens on a CRBR-S.

The three mod kits

Some zombies drop mod kits. Picking one up converts the weapon; picking up the same kit again refills it, and when a kit runs out of ammo the weapon goes back to its base form. There is no way to choose which kit drops.

Blazer

An assault rifle that fires a concentrated blue beam, 40 rounds a magazine. The main quest needs it to melt a reinforced wall.

Diffuser

A shotgun that fires five green energy projectiles in a horizontal line, 30 rounds a magazine.

Swarm

A handheld launcher that fires two twisting yellow explosives in rapid bursts, and locks onto enemies through its own sight.

Pack-a-Punch

Upgraded, the CRBR-S becomes the CRBR-TRN Duality, with more damage and ammo. A mod kit put on an upgraded weapon is upgraded too: the Blazer becomes the Enlightenment, the Diffuser the Quintessence and the Swarm the Seeker.

CRBR-TRN Duality

The upgraded pistol, here at its first tier.

In the First Room

The quest needs Klaus and the hotel, and the Mystery Box has no spot in the First Room according to the Call of Duty Wiki. In a doors-closed game, the CRBR-S is out of reach.