Here is the full list of all 20 Steel Ocean achievements.
Survive 10 battles.
Sink 10 Destroyers.
Win 1 battle.
Win 20 battles.
Sink 10 Submarines.
Sink 10 light cruisers.
Sink 10 heavy cruisers.
Sink 10 Battleships.
Sink 10 Aircraft Carriers.
Sink one ship of every type in a single battle.
Sink Pennsylvania using a Japanese carrier's dive bombers.
Sink Yamato using a U.S. carrier's torpedo bombers.
Complete: Pacific Beast, Allied Fleet Pride, Mobile Nation, and Unsunken Archipelago.
Get 5 "Hero" Medals.
Research a Lv8 destroyer.
Research a Lv9 heavy cruiser.
Research a Lv9 battleship.
Research a Lv9 aircraft carrier.
Research a Lv8 submarine.
Sink 10 enemy ships with a Lexington's main artillery.