In World War II, high frequency direction finding (HF/DF or "Huff-duff) was used by Allied escort vessels to detect submarines making position or sighting reports. The direction finding technology was not thought feasible for installation on a warship by the Kriegsmarine and they attributed successes of Huff-duff to radar technology of a performance that did not exist at the time. The standard escort tactic was to steer at speed in the direction of an HF/DF bearing until the target submarine was sighted (often visually, but sometimes on radar) and open fire before the submarine dived. If the submarine dived before being shelled, it could be hunted on sonar.