The Mortars Ultimate Plan is inside an underwater chest at Antocha Wreck, a Diving Bell location northeast of Great Inagua, around coordinates 600,636.
This is a short ship-plan pickup, but it is easy to chase the wrong wreck if you sail there before the dive activity is available. The important split is simple: get access to Antocha Wreck, loot the underwater chest, then handle the actual Mortar IV purchase separately.
Antocha Wreck location and Diving Bell requirement
| Detail | Answer |
|---|---|
| Plan name | Mortars Ultimate Plan |
| Location | Antocha Wreck |
| Approximate coordinates | 600,636 |
| Requirement | Diving Bell |
| Nearby landmark | Northeast of Great Inagua |
KEY!You need the Diving Bell before you can access Antocha Wreck. It unlocks through Diving for Medicines, Sequence 6, Mission 1, after which the wreck can be used as a Diving Bell activity.
Use 600,636 as the practical map point. The same wreck marker can appear a few coordinate points off on different maps, but the target remains Antocha Wreck, northeast of Great Inagua.
How to get the Mortars Ultimate Plan in Assassin’s Creed IV: Black Flag
The pickup is a quick Diving Bell activity once the Antocha Wreck marker is available.
STEP 1/6
Sail to the bell location
Go to the Diving Bell marker in the northeastern section of the map, just above Great Inagua.
STEP 2/6
Approach the activity rack
Move up to the rack at the wreck site to begin the diving activity.
STEP 3/6
Enter the Diving Bell activity
Start the activity prompt so Edward is placed into the diving bell.
STEP 4/6
Go underwater
Use the bell to descend into the Antocha Wreck dive area.
STEP 5/6
Swim through the wreck area
Head through the underwater wreck site toward the chest tied to the plan.
STEP 6/6
Open the chest
Loot the underwater chest to receive the Mortars Ultimate Plan.
Video help
What the Mortars Ultimate Plan changes at the Harbourmaster
| Requirement | Amount |
|---|---|
| Mortars Ultimate Plan | 1 |
| Reales | 25,000 |
| Metal | 650 |
KEY!The Mortars Ultimate Plan opens the final Mortar IV upgrade option for the Jackdaw; it does not install the upgrade by itself. After the chest is looted, buy the upgrade from a Harbourmaster once the purchase requirements are ready.
Costs can vary by release, but in Black Flag Resynced the Mortar IV purchase uses the following requirements.
Antocha Wreck mistakes that waste time
The main miss at Antocha Wreck is checking the first debris field and assuming the chest must be near the bell. The correct target is the southern shipwreck, not the northern wreckage or the bell platform.
Use the air barrel as your cue: it marks the broken hull opening that leads to the Mortars Ultimate Plan chest.
Two other blockers are simpler. If the activity is missing, you are too early for the Diving Bell; if the Jackdaw does not improve after looting the chest, you still need to pay for Mortar IV at a Harbourmaster.
Frequently Asked Questions
Where is the Mortars Ultimate Plan in Black Flag?
It is at Antocha Wreck, the shipwreck dive site above Great Inagua. Use the wreck name on the map first and the coordinate readout second.
Do you need the Diving Bell to get it?
Yes. Antocha Wreck is a Diving Bell activity, and the Diving Bell comes from Diving for Medicines in the main story.
Which chest has the Mortars Ultimate Plan at Antocha Wreck?
The plan is in the underwater chest inside the southern shipwreck. If you are searching around the bell or northern wreckage, move toward the southern hull instead.
What does the Mortars Ultimate Plan unlock?
It unlocks the final Mortar IV upgrade tier for the Jackdaw, making the last Mortar upgrade available through the Harbourmaster upgrade menu.
Why is Mortar IV still unavailable after finding the plan?
You may still be missing 25,000 Reales, 650 Metal, or the required Harbourmaster setup at Great Inagua. The plan is only the blueprint gate; it is not a free upgrade.
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