'Using SMGs, kill 50 Tempests within 2 seconds of them reappearing after teleporting.' Here's how to unlock it via Black Ops Cold War zombies mode: 'Using SMGs, kill 3 enemies affected by your Tactical Equipment in 15 different completed matches.' In Black Ops Cold War's multiplayer, the OTs 9 is unlocked with the following challenge:
And the Black Ops Cold War challenge for the recently-released OTs 9 left some players frustrated due to its difficulty. It's as simple as that, except it's not always simple to unlock these weapons.