The tactical nuke contract appears to your team right as you start the game while waiting within the plane. In order for the contract to appear on your map you must win five games in a row (Warzone games).
Moreover, there will be three locations on your map highlighted in a massive, bright orange icon(s). These are bomb components. You must, with your team, acquire all three bomb components. Carrying these components provides negative bonuses to your team.
After 10 minutes and 30 seconds of holding these materials, a bombsite will be revealed and your team will have to arm the nuke with the materials previously mentioned.
Once armed, you will have to defend the nuke for two minutes. If you accomplish this, not only will the nuke end the game and your team will win– but you’ll have some bragging rights.