The lenght of the torpedotube is only one variable in regards to being able to launch torpedoes... In fact, there's no problem launching a torpedo which is longer than the tube - especially for a surface tube, but it would also be possible (in theory) from a submerged tube.
The main problem is that different manufacturers/nations had different designs of the torpedo, with different placements of the acessports for setting speed, depth, runningdistance and (most important) the starting lever.

All german WW2 torpedoes had a starting lever being pulled back by a lever inside the tube as the torpedo starts to move forward.