Here is the full list of all 8 Silent Depth 3D Submarine Simulation achievements.
Sink 4 freighters
Sink 2 freighters and 2 tankers
Sink 2 destroyers and 1 freighter
Sink 1 light cruiser, 1 destroyer and 1 freighter
Sink 1 carrier, 1 freighter and 1 tanker
Sink 2 gunboats and 1 destroyer
Sink 2 carrier and 1 troop transport
Sink 1 battleship, 2 destroyers and 1 troop transport