The Hull Armor Ultimate Plan is in an underwater chest at the diving-bell marker in the top-left corner of the map; start the dive, swim through the small archway, and the path leads straight to the chest.
If your ship upgrade is blocked because it needs the Hull Armor Ultimate Plan, the route is short once you are at the right marker. The only real trick is finding the correct bell icon on the map, then following the underwater path cleanly.
Hull Armor Ultimate Plan map location
Go to the top-left corner of the map and look for the bell icon. That marker is the diving-bell activity tied to this plan chest.
How to reach the Hull Armor Ultimate Plan chest in Assassin’s Creed IV: Black Flag
This route takes you from the map marker to the underwater chest that holds the plan.
STEP 1/6
Find the bell icon
Head to the top-left corner of the map and select the bell icon there.
STEP 2/6
Arrive at the diving-bell marker
Come to that location and begin the activity if this is your first time using it.
STEP 3/6
Go underwater
The activity sends you underwater through the diving bell.
STEP 4/6
Follow the underwater path
Swim forward along the route shown after you arrive below.
STEP 5/6
Pass through the small archway
Swim through the small archway in the path.
STEP 6/6
Open the chest
KEY!Continue straight to the chest at the end and open it to get the Hull Armor Ultimate Plan.
Use the small archway as your landmark; once you pass through it, the route takes you directly to the plan chest.
Video help
Hull Armor Ultimate Plan ship upgrade use
The Hull Armor Ultimate Plan is needed for upgrading your ship. That is why this particular chest can become a roadblock: the upgrade path asks for the plan, but the chest itself is tucked behind a diving-bell route instead of sitting on land.
After collecting it, return to your ship upgrade flow and continue from the requirement that was holding you up.
Frequently Asked Questions
Where is the Hull Armor Ultimate Plan located?
It is inside an underwater chest connected to the diving-bell activity in the top-left corner of the map.
What map icon should I look for?
Look for the bell icon. That is the marker for the diving-bell activity that leads to the plan.
Do I need to start a diving-bell activity?
Yes. If you have not done that activity before, you need to start it when you arrive at the marker so Edward can go underwater.
What underwater landmark leads to the chest?
The landmark to watch for is a small archway. Swim through it, then keep going to reach the chest with the plan.
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