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