As with the previous mission, this memory sequence has us plundering vessels in the nearby area. This time though, our target is metal. Unfortunately, this resource is not carried in great numbers by merchant vessels, but is much more common on military ships. The problem with this area is that there are lots of merchants and little military presence.
To have the military appear in the area, we need to plunder a few of the merchant ships in the area to build up your notoriety (indicated by the red crossed swords above the ship health bar). Note that there is an optional objective to loot at least 30 Sugar, so try targeting vessels carrying sugar during this early stage to knock the objective over as soon as possible.
After boarding and plundering 2-3 merchants, a Brig or two will show up. It should be noted that they are much more powerful than the merchant schooners you have been targeting and have more advanced weapons and armour. As with the other types of ships, getting it to low health will allow you to board it. Do so to plunder all of that metal that it is stashing.
Continue to attack and plunder brigs until you have all the metal that you require. At this point, the game wants you to return to Salt Key. Instead of going right away, due to attacking the military vessels you will be well and truly notorious. As such, there should be a hunter ship in the area (these are marked by the red crossed sword icons). Track it down, incapacitate it and plunder it to complete the second optional objective.
Return to Salt Key. Run over and speak to the local officer indicated on the mini-map. Bribe him for 200 Reales and this will reduce your notoriety. Handy for future reference!
After chatting with the officer, make your way back to the Jackdaw, enter the captain’s cabin and interact with the model ship on the desk to the right. This acts like your own personal on-board Harbourmaster. We need to purchase the broadside cannons ship upgrade from here to complete the mission.