The periscope did have a lock. It just was not locked on the target, it was locked to a fixed position in space. This was the firing position point, as the solution was plotted in, this solver position was the aiming point. As the ship moved into the aiming reticle ( usual to chose the just before or after the funnel wanting to destroy the ships vital machinery ) the torpedo must be fired! The Hydrophone notes were kept for submerged attack he could update changes in a low light condition not seen right away that are crucial. The real data kept there was the speed calculated by revolutions per minute. Often the only way to calculate speed of a target at night. In any of our super mods so far the periscope has not been accurate enough for realistic manual targeting. For one there are two visible azimuth indicators visible in the ocular view. One the fixed "0" of the bow, and two relative bearing of the periscope one above the other. ( photographs included in the link provided ) the wrongly identified "observation periscope" is actually the Night Periscope. Its broader head collected as much light as possible giving better options for a night shot but never perfect as sometimes no shot was possible. Here is a link to the best research ever done on the TDC and the Attack and Night Periscopes and the advanced Properties contained in them and many of the pre-solved firing solutions for set angles of attack if the TDC was inoperable.
http://tvre.org/en/aiming-with-the-periscope Realism mods always intrigue me, sometimes I have the time to just sit and forget the clock in SH3. I sat for 6 hours real time just getting depth charged once.