* "Find a rebreather."

* "Find the cartel warehouse key from the easternmost sunken ship in Al Mazrah."

* "Find and extract the cartel laptop from the warehouse."

The Phalanx DARK WATER Mission features a 3step series of tasks that requires a little looting, a little diving underwater, a little shipwreck exploration, and a little good fortune on exfil.

First, "find a rebreather." This process is a little luck of the draw, but you can usually find the rebreather easily when searching anywhere in AlMazrah. In this video, I already had one from a previous attempt at this mission, so it doesn't show where to find them. (They can also be crafted from "Imported Tea" plus a vanilla "Hard Drive" at buy stations, but I do not know if you get mission credit for that. Crafted rebreathers only give you one "puff" of fresh air, while ones you find have four.)

Second, "find the cartel warehouse key from the easternmost sunken ship in AlMazrah." You WILL need the rebreather for this; the length of the dive is too long to survive without at least one "puff" from the oxygen bottle. (To use the rebreather, equip the rebreather, which replaces your active weapon; then push the fire button to take a breath.)

This is shown in detail in the video: Enter the wreck from the hole in the side of the hull. It faces northwest, so you'll be facing southeast to enter it. (Don't be confused by the hole found in the bow of the ship!) Once inside, turn left immediately and go through a hatch; then immediately turn right into the next hatch. After the second hatch, turn left again and you'll see a workbench along the northeast wall of the room. The "Cartel Warehouse Key" is on the right side of the workbench.

Lastly, "find" and "extract" the cartel laptop. These are very much two separate tasks. The "warehouse" is labeled as the "Kushaak Construction" building in Hafid Port, closest to the southeast corner of the largest warehouse building at the port facility (the one with the submarine inside); you can see which one from the minimap in the video. Unlock it with the "Cartel Warehouse Key" and find the laptop on a shelving unit in the southwest corner of the building.

I got lucky in the video; there was an exfil right there at Hafid Port. Your mileage may vary. Get out! Extraction is required for mission completion.