What explains the rise of maritime private military security companies (PMSCs)? How do they differ from land-based PMSCs? I argue that PMSCs have become major providers of security at sea. Yet maritime PMSCs are not hired by states but by the maritime industry. The United States and allied forces do not guarantee merchant vessels’ day-to-day security. Consequently, shipowners rely on PMSCs and war and piracy insurance to operate their vessels in dangerous waters. The United States, however, plays a vital role in regulating PMSCs and creating environments in which PMSCs can operate effectively. This paper shows that order at sea depends not on the United States’ “hard” naval power but on its leadership in global governance and on its ability to create rules and norms for maritime behavior. It also shows that PMSCs can help secure the oceans if regulated and supported by state authorities. I illustrate this logic through three case studies of how the United States has facilitated private security efforts: during the Iran–Iraq Tanker War, in piracy-prone shipping lanes off Somalia, and in the Persian Gulf following attacks there in 2019.