Crazy Eddie wrote:
Which, like the teeth of a cornered rabbit, is not their intended use, nor is it even their typical use, and as per the examples you cited, turned out to be a highly ineffective use after all.
Your definition of highly ineffective is either off or you just didn't bother to read the articles. Stern tubes were of use to discourage and potentially sink pursuing ships. The intended use of a torpedo is to sink the enemy ship. Firing your stern tubes at a ship behind you works for using it to discourage pursuit either by forcing the enemy to evade or by sinking them outright. Obviously stern tubes could also be used for attack as the sub turns to leave and open distance after attacking with her bow tubes.
The U-85 missed with her stern torpedo and was eventually sunk.
The Tang successfully used her stern tubes against ships that attempted to ram her and also against a destroyer firing on her as she was making her escape.
The O-21 used her stern torpedoes against the following, then pursuing U-95.
The Spadefish missed with her stern torpedoes but forced a destroyer to zig and attempt to depth charge her but she escaped.
Also interestingly, the Germans thought of using torpedoes to take out escorts. They had some kinks to work out but apparently got it to work near the end of the war.
The Zaunköning (Wren) came into service during the autumn of 1943. Intended to be an escort-killer, it achieved some early minor success only to be countered by the allied Foxer noise-making decoy. It was scoring hits against escort and merchants to the end of the war though.
The weapon was designed to lock onto the loudest noise after a run of 400m from its launch. This often proved to be the U-boat itself and standard issue-orders were to dive immediately to depth of 60m after launch from a bow tube while a stern shot was to be followed by a complete silence in the boat.