Season 1 of Warzone 2.0 and Modern Warfare 2 brings four new weapons to unlock, including the M13B assault rifle.

The new assault rifle is part of the Bruen Ops platform, alongside the new BAS-P SMG and Chimera assault rifle that is arriving mid-season. It boasts a high fire rate and low recoil, in addition to its own set of Base camos that can be used across all weapons in the game.

The good news is that the M13B can be unlocked for free, but it is tied to a challenge specific to the DMZ exfiltration mode.

Here’s how to unlock the M13B assault rifle.

How to defeat the Chemist in DMZ and unlock the M13B assault rifle

Call of Duty Modern Warfare 2 Chemist DMZ radiation zone
Screenshot by Koh Wanzi/ONE Esports

The M13B is unlocked by defeating the Chemist in the radiation zone of DMZ and extracting his dropped weapon.

The radiation zone is marked by a yellow circle on the Tac Map (press “M”), complete with a hazard symbol for ionizing radiation.

This is a PvE boss battle that is actually fairly challenging, and you’ll probably want to tackle it as a full squad of three. You’ll also need to acquire gas masks for your squad first before starting the fight, because the radiation zone will damage your squad over time.

Gas masks can be found as ground loot in the DMZ, but they are rather rare. Alternatively, they can be purchased for $2,000 at a Buy Station.

Once you have the gas mask, you can either extract from the DMZ or head to the Chemist. The safer option is to exfil first, so you can add the mask to your stash and return later. If you die, you lose the mask and have to start all over again.

You also have to be the first squad to defeat the Chemist, which means another team may have beaten you to it already, depending on how long it took for you to secure the masks.

Call of Duty Modern Warfare 2 DMZ Exfil
Screenshot by Koh Wanzi/ONE Esports

Exfil locations are marked by a blue exit icon, resembling a figure running toward a door. A helicopter will then arrive to ferry you away. However, do note that the helicopter will not leave until the countdown timer expires, and AI soldiers will attempt to prevent you from extracting.

The second time you drop to the DMZ, you can head straight to the Chemist with your gas mask and insured primary weapon. We recommend finding a vehicle and driving to the hazard zone to ensure you get there as quickly as possible.

The Chemist can be identified by the yellow hazmat suit he wears — if you drove there, running him over with the vehicle is also one of the quickest ways of taking him down. Once you defeat him, he will drop the M13B blueprint.

Call of Duty Modern Warfare 2 Warzone 2 DMZ Chemist
Credit: The Gaming Merchant

Only the player holding the blueprint will receive the weapon, so only one player can extract with the M13B and unlock the weapon.

But if you already have a friend that unlocked the weapon, you’re in luck. All you have to do is load into the DMZ, have them drop the weapon, and then exfil while holding it. Alternatively, you can also pick up the weapon from enemy players.

There is currently no path to unlock the M13B in multiplayer or Warzone 2.0. That may change in the future, but the DMZ is your only route for now.

Learn more about the best guns to level for Warzone 2.0, the new Gulag, and the best muzzle attachments to use.

READ MORE: What is DMZ? Warzone’s new mode detailed