Way to unlock: You need to complete Main mission 30 (Scouting the Port) and wait until you are texted by Wade. This will result in the appearance of the Hs marker on the world map, which marks the place where you can find the sub.
Playable characters: Trevor
Additional information: The most important piece of information, in connection with this mission, is that it is common for both variants, i.e. the attack on the freighter and the attack offshore. Stealing the sub is an easy task but, it is a good idea to seize the opportunity and learn its controls while hauling it from the water. Furthermore, I recommend that you take a suppressed sniper rifle along.
The sub is in the docks, in the South-Eastern part of Los Santos and it is attached to a large ship. After you get there, get out of your car and stop in the spot shown in the screenshot, from which you will have perfect visuals on the sub.
In accordance with the previous suggestion, select the sniper rifle from your inventory and start aiming at the lines that the sub is suspended on. You need to hit all four of them, thanks to which the sub will detach from the vessel. Jump into water and swim up to the sub (Submersible) and get onboard.
You can now steer to the point where the sub will be pulled out of water, and it is located to the West of here. I recommend that, during your journey there, you learn exactly how the sub is controlled and stay well above the bottom, thanks to which you will prevent bumping into obstacles, which unnecessarily makes the mission longer. After you approach the destination, you will notice a yellow circle in the distance, which is where you need to deliver the boat.
Wait for the sub to be transported onto the truck bed, het into the truck and drive towards the warehouse to the West of the port that you visited in the previous mission. Stop the truck in the marked area, which will conclude this mission.
Rewards for completing the mission: none
Requirements for the completion of the mission in 100%:
- Mission Time - you need to complete this mission within 8 minutes and 30 seconds. Make sure that you, predominantly, do not bump into obstacles while onboard the sub.
- No Boarding - you need to steal the sub without coming aboard the vessel that it is attached to so, take all the steps included in the above description.