[BigWalleye]

This Four-Bearing Method is useful for detection and approach, not for engagement. It is used to determine range, course, and speed with precision adequate to position the sub for a visual firing setup.

USN doctrine in the 1930's did suggest hydrophone-only engagement of capital ships in task force strength. USN believed that ASW defense might prevent the sub from reaching a firing position using periscope observation. Once the US entered the war, this was quickly proved wrong on two counts: First, IJN ASW defense was not that strong. And second, submerged firing based on hydrophone contact alone was so inaccurate as to be a waste of torpedoes. IIRC, there was never a EDIT: only one successful hydrophone-only attack made by any submarine of any nation during the war.

Fnally, while this was the pre-war doctrine of the USN, it was never shared AFAIK by the KM. The KM's most favored tactic was a night surface engagement, and hydrophone-only attack was never encouraged. I don't know that it was ever even tried by a German sub.

Use the Four-Bearing Method to set up your approach. The hydrophone is effective at 30+ km, generally farther than visual range in the ATO. Derive your firing solution from visual contacts at closer range. That is how it was done historically.