This chapter draws out international laws applicable to ensure the navigational safety of submarines and to establish what laws apply when a submarine is ultimately lost at sea. The discussion is concerned with both military and private submarines during times of peace. To avoid collisions, submarines must account for surface traffic as well as submerged traffic and deploy appropriate signals and sounds. Submarines prompt distinct questions with regards to navigational safety. Where a submarine is in distress and ultimately sinks, consideration is further needed as to international law rules on search and rescue, as well as the law of wrecks and possible salvage. For submarines that have been lost at sea for a long time, safeguarding underwater cultural heritage may become a key consideration. When lost at sea, the relevant laws are comparable to other ships or warships but the difficulty rests in the interaction of those rules.