How to unlock the OTs 9 in Warzone
The OTs 9 can be unlocked either by completing an in-game challenge or by purchasing blueprints in the shop.
The weapon has two different challenges, depending on whether you're opting to unlock it on Black Ops Cold War or Warzone, listed below:
How to unlock the OTs 9 in Warzone: Kill 2 or more players rapidly in 15 different completed matches, using any SMG
How to unlock the OTs 9 in Black Ops Cold War: Kill three enemies affected by your Tactical Equipment in 15 different completed matches, using any SMG
Neither of these tasks are particularly challenging, but they can be rather time-consuming due to the amount of matches required.