Greylorm is a hidden boss that can only be spawned and killed while inside the Aether Storm in Call of Duty: Modern Warfare 3 (MW3) Zombies. Read on to learn how to summon and how to beat Greylorm, the best gear to bring, as well as the rewards for beating it!

How to Summon Greylorm

Collect Calibration Data USB Sticks

Before you can summon Greylorm, you'll have to collect four Calibration Data USB sticks: Alpha, Bravo, Charlie, and Delta. Since their spawn locations change per match, you'll have to check their location data posted on a wall at the second floor of a building in Orlov Military Base.

All Calibration Data USB Locations

Activate Refractors in Aether Storm

Once you have all four Calibration Data USB sticks, look for the Refractor Location on your Tac-Map. While these machines don't have unique icons, they always spawn beside two ammo caches that are easy to spot in-game.

Wait for the Aether Storm to expand until the Refractors are inside the storm (happens after 40 minutes have passed), then insert the Calibration Data USB sticks in the console to activate them.

This will cause the Greylorm to rise up from the ground after a short amount of time, so use this brief interlude for your squad to prepare!

All Refractor Locations

How to Beat Greylorm

Greylorm Boss Fight Tips and Strategies
Shoot at the Red Aura Use Decoy Grenades to Lure Zombies Away Repair Gas Masks at Ammo Cache Parachute if it Throws You in the Air Stay Away When it Slams the Ground

Shoot at the Red Aura

The Red Aura sticking out of Greylorm's scales is its main weakness. Focus all your firepower at it to damage Greylorm effectively and quickly reduce its HP.

We strongly advise that you and your team should bring a weapon with Legendary rarity and Pack-a-Punched to Level 3 for maximum damage output.

Use Decoy Grenades to Lure Zombies Away

Decoy grenades will come in handy to lure zombies away from you as they'll constantly spawn out of nowhere and interfere with your fight with Greylorm.

These decoy grenades will also become useful to keep the zombies from ganging up on you should you need to revive a fallen teammate during the boss fight.

Decoy Grenade: How to Use and Unlock

Repair Gas Masks at Ammo Cache

Gas Masks will continuously deteriorate while in the Aether storm, but they can be fully repaired at Ammo Caches located around the battle zone.

Since Ammo Caches have a cooldown after each refill, a great tip is to repair your gas mask once it's at 2 bars since by then, the Ammo Cache would probably be available already after your previous usage.

How to Get Gas Masks

Parachute if it Throws You in the Air

Once Greylorm burrows itself underground, it will relentlessly chase down players, and those unforunate enough to get caught will be thrown high up in the air.

When this happens, don't forget to deploy the parachute to avoid taking fall damage and getting instantly downed. It would also be best if you reposition yourself to a safe distance while parachuting down.

Stay Away When it Slams the Ground

Keep your distance when Greylorm starts slamming the ground consistently as you'll be eaten if you get caught in the middle of it, resulting in an instant death.

Greylorm Fight Best Gear to Bring

Golden Armor Plate

The fight with Greylorm is a tough one, so you'll want to equip a Golden Armor Plate as it regenerates armor plates automatically over time.

You'll also want to use this with a 3-Plate Armor Vest to further prolong your survivability.

How to Get Golden Armor Plate Schematic

Durable Gas Mask

While the regular Gas Mask provides decent protection in the Aether Storm, the Durable version (purple color) has more health and durability, making you last longer in the Aether Storm and lessen the need of having to repair your gas masks at Ammo Caches frequently.

Sentry Turrets

Deploy Sentry Turrets around the vicinity of Greylorm as they'll assist you in dealing damage to it and speeds up the process of killing Greylorm. We recommend bringing in 2 or more Sentry Turrets for maximum efficiency!

How to Get Sentry Guns

Juggernaut

The Juggernaut comes with a minigun that has an ultra-fast firing rate and superb damage, as well as an armor suit that increases your defense greatly. This lets you damage the Greylorm effectively while also being able to tank a few hits from it.

How to Get Juggernaut

Greylorm Rewards

Schematic Rewards

Modern Warfare 3 (MW3) Related Guides

Zombies Mode Walkthrough and Guide

All Zombies Guides

Zombies Season 1 Guides