Ultra Maritime demonstrated a counter-unmanned underwater vehicle (C-UUV) capability during the US Navy’s Lanternfish 2026 exercise. The sonar was able to detect and classify autonomous undersea threats in a realistic port protection mission setting. What happened at Lanternfish 2026 Lanternfish is a multilateral naval exercise focussesing on critical undersea infrastructure protection and emerging autonomous vehicle threats. During the exercise, Sea Spear consistently detected, tracked and classified medium- and large-diameter UUVs. The broader engineering challenge of autonomous undersea threat detection connects to developments in machine learning-based acoustic classification and distributed sensor networks.