Here is the full list of all 20 Steel Ocean achievements.
Win 1 battle.
Win 20 battles.
Survive 10 battles.
Sink 10 Submarines.
Sink 10 Destroyers.
Sink 10 Battleships.
Sink 10 light cruisers.
Sink 10 heavy cruisers.
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.