Are magnetic anomaly detectors still useful for ASW?

Are magnetic anomaly detectors useful in modern anti-submarine warfare?

Yes. They can reveal a magnetic disturbance consistent with a submarine, and in rough sea conditions may be one of the more reliable detection methods, but they do not by themselves provide a perfect identification.

The detector looks for local variation in the Earth's magnetic field caused by a large metal object. Installations appear on helicopters and fixed-wing patrol aircraft such as the P-3 Orion, typically on a boom away from the airframe's own interference. A contact may instead be a geological structure, especially if it does not move, so crews must combine the reading with other sensors and tactical context. Submarines can exploit known wrecks or geological features to make that ambiguity work in their favor.