"Increased weapon handling. Serum reacharges over time"
— In game description
Catalyst is a basic training perk featured in Call of Duty: WWII. The serum lasts for 10 seconds, has a 20 second cooldown (which starts after the serum has expired) and has powerful effects. It increases the fire rate of weapons by 30%, reduces hip fire spread by 50% and increases reload speed by about 40%. The additional fire rate stacks with Rapid Fire, the reduced hip spread stacks with Steady Aim (attachment) and technically, the increased reload speed stacks with Hustle.
When used wisely and with fast firing weapons such as the MG42 or MG15, the serum will allow the player to mow down multiple enemies at once with ease.