Evade Collision Attack: Control Tower + Special Rudder
Direct Hit Prevention: Control Tower + Mast Top
Watertight Bulkhead: Anti-skid Rope + Hull Bulkhead Plating
Command Post: Control Tower + Admiral's Cabin
Reaction Rudder: Metal Work + Special Rudder
Attack Prevention Net: Casting Net + Admiral's Cabin
Improved Gun Port: Admiral's Cabin + Munitions Chambers
Armouring Deterioration Bullet: Special High Explosives + Metal Work
Guilder 02-23-2025
Yggdrasil update added this to Optional Skills: Improved Deck