An underwater sound velocity meter is described which employs an open‐end heavy‐walled tube for a resonant cavity. The water column is excited into vibration by a sound source near one end, while a hydrophone probe at the tube center registers the pressure amplitude. A sharp resonance (Q=450) permits making relative measurements with an uncertainty of less than 0.2 m/sec when the fundamental mode (f≈570 cps) is used.