Difficulty: Easy
If you're bad at moving and shooting you'll want a machine gun equipped as that's a big part of this mission.
Shoot the explosive barrels where possible to make things easier.
When fighting Irving at the end you'll need to shoot his tentacles before they squash you and hit the lump on the top of the big creature's head. That's the weak point.
After taking a lot of damage the creature will open it's mouth to reveal Irving. Irving is now the weak point, so take advantage of the rocket launcher turrets available.
Note: If you're struggling there's a First Aid spray at the front right of the boat.