This page is a walkthrough for The Doomsday Heist Setup Mission, Submarine Recon. It’ll navigate you through the necessary steps to successfully destroying all the Sea Mines.
Use the strombergs to destroy a convoy before heading underwater to scan the submarine.
Destroy the sea mines / Scan the Submarine
Once you’ve started up the mission, take the stromberg and follow the waypoint to North Chumash. Upon arrival, use the missiles and destroy the incoming convoy, then follow the next waypoint Paleto Bay or Paleto Cove.
Enter the water and press [Right D-Pad] to stick the Stromberg into Submarine Mode. Now drive over to the red markers and use Torpedoes to destroy 10 Sea Mines. Once completed, approach the submarine and scan the front, middle, and back parts of the submarine.
If you’re on the other team, then you’ll need to approach the wreckage and scan it, then return to land and take the Strombergs to the drop off to complete the mission.