That's what is most interesting. We're to believe that sonar only was "accepted doctrine" based on what? If everyone was expected to do it, the instructions should be easy to find. After all the
Submarine Torpedo Fire Control Manual tells intricate details about every other known attack method, allowing us to perform them with great fidelity to the original submarines.
But there is not one word of information about attacking with sonar only. If it were a valid attack method that did not work, they would likely have included it for future reference and possible refinement into a technique that DID work. But instead we have not one word of reference to this "standard accepted doctrine" in a book whose purpose was to train sub officers in "standard accepted doctrine."
It seems VERY unlikely to me that a universal doctrine would escape all notice in the standard reference on submarine tactics. They would at least have mentioned and outlined the technique while explaining that visual firing methods have proved much superior.
So something doesn't add up here. There is a disconnect from what we have been told to the actual training materials of the time. It's probably useless after 60 years to speculate why this is the case.