Ch 9.
With Nami and company manning the Sunny they believe they have the advantage as they begin to drop the teams off in their assigned areas. It could not have happened at a more perfect time as the assault begins as the last team is getting in place.
Ussop "Is anyone else seeing what I am seeing?"
Nami "Yeah they are incoming and its as bad as we had thought."
We see this massive army of Grimm clearly under someones direction as they are built much like an army would. It's full of death stalkers, goliaths, beowolves, and ursa's as far as the eye can see. The sky is filled with lancers. When he see's this Iceberg heads over to the weapons control console tells everyone on board he is turning the new weapons system on, then he flips the switch and like magic the Sunny gets belt fed 50 caliber machine guns that run up the metal between the glass on the new glass dome over the top of the ship at every joint leaving Nami with a clear view but also protecting the crew. At this same time the new cannons deploy and suddenly the Sunny becomes a flying fortress that can not be approached without massive losses.
The evacuation begins and everyone is trying to hurry people along given the number of grimm being far more than anyone was expecting. The walls are holding for now and the people are evacuating and this is when the unexpected happens…
Right in front of the bullhead bay the ground suddenly opens up and we see these burrowing worm style grimm appear out of the ground sending everyone in line rushing towards Bartolomeo and the bullheads. Zoro runs out and begins to cut them down while Coco and Elm are trying to keep everyone organized and moving. It's at this point that the Lancers launch their attack and begin swarming through the city. Ussop is launching attack after attack and the Sunny is making strafing runs trying to keep the citizens alive as much as they can.
Ussop "Whitebeard Ace we need some more air support can you guys take a bite out of the skies?"
Whitebeard "yeah I can do that Zoro has things under control here at least for now."
Ace "Yeah I can do some of that while sticking with my team I can make that work."
Ace starts sending fire balls into the sky trying to thin out this seemingly unending swarm. Whitebeard sends shockwaves through the sky wiping out swaths. No matter how many die they just keep coming and this keeps going on for a half an hour before finally the majority has been evacuated and the straw hats can really begin to fight unrestrained. It couldn't have happened at a better time either as while the grimm may be thinning out or so it looks suddenly we see a wyvern and 5 nukalevee are seen approaching. When this is seen Ironwood demands that they leave now as even as strong as the strawhats are he is rightfully terrified of this. This is a kingdom killing army and it has finally revealed it's trump card. While this is not what Luffy and company want to do they see the mission is done and they resolve to regroup and make a new plan.