Each modification has a set of regular upgrades (the picture above shows Energy Efficient and Light Weight upgrades).Unlock new modifications by finding Field Drones. Every weapon in Doom has one or two modifications - for example, Gauss Cannon has Precision Bolt and Siege Mode (presented in the picture above).Remember to switch between weapons and try to use those that have reached their current ammo limit. However, you can increase your limit by finding Argent Cells. You can carry a limited amount of ammo.You can switch between them by using the wheel menu. The Doom Marine can carry all of his weapons. Every newly acquired weapon is added to your inventory permanently.Also, some of them can be found earlier thanks to exploration. The most important ones are obtained in specific parts of the game. Doom's campaign offers 10 weapons and 3 types of grenades.
