That’s kind of a problem with how you define “find”. Until around the time the Titanic was found there wasn’t really the technology to gather anywhere near the kind of information about location and condition of deep sea wrecks. Obviously it was fairly well known, for example, where the Titanic was or he’d have never “found” that wreck either.
True, he would’ve had to have “found” the subs in some sense first before he could examine them with his gear. Even knowing their location it isn’t simple. It’s not like have the GPS coordinates of a gas station and simply driving over too it. It is more like flying your helicopter to the coordinates at an altitude of 10 to 15 thousand feet, then dangling a camera on a wire and trying to find the station...