Sonar and Undersea Sensing

Sonar is the underwater analog of radar, but with distinct physics: sound moves slower than radio, the ocean is a complex refractive medium, and stealth in the water is substantially about acoustic signature control. Two families dominate: active sonar (pings the water, listens for returns) and passive sonar (listens for adversary noise without revealing its presence). Modern undersea sensing extends beyond hull-mounted arrays to towed arrays, ocean-bottom networks (IUSS SOSUS successor), and unmanned undersea vehicles. Quantum magnetometry (see quantum_sensing) is emerging as a complementary undersea detection modality. Publicly-known suppliers of undersea sensing systems include Ultra Electronics, Thales, Lockheed Martin, RTX, and DRS.