Type 177

This hull-mounted, medium-frequency sonar was approaching obsolescence but, until not long ago, remained in service with several navies. The sonar scanned a 360-deg area around the ship, and had a range of 3.2 nautical miles (6,000 meters). It was the first British scanning sonar.

It uses a flat sector-scanning transducer producing five 10-degree transmitting beams in a ripple sequence. It cannot track fast submarines and was replaced in the British Royal Navy by the Type 184....