Here is the full list of all 12 Iron Sea Defenders achievements.
Destroyed 20,000 enemies throughout the entire game.
Collected 10,000 coins in a single level.
Completed a level without improving weaponry.
Placed all types of weaponry accessible in the episode on a single tile.
Installed all types of weapons accessible on a level.
Used bonuses 10 times on a single level.
Used all the different types of bonuses on a level.
Sold 10 weapons on a single level.
Place all towers available in the episode
Completed a level with the time machine's health below 10 points.
Didn't let a single enemy reach the fort throughout a level.
Unlocked a tile for anchors on any level.