[perisher]

Historically, WW1 and just after, as subs got larger they had tubes facing all directions, including beam tubes (these could not be reloaded at sea). Pretty soon the beam tubes were dropped as a bad idea. (Difficult to use and took up a lot of space). Many navies kept the stern tubes, they could be useful but they were much more difficult to use than the bow tubes. The problem was getting a good angle while moving away from your target. Eventually everyone dropped the idea. First to lose it were the British, although the S and T class boats retained an external stern tube. That is, of course, a one shot only tube. As built the T class also had two rearward firing external tubes mounted one either side of the conning tower. These were turned around in a field mod and made to shoot forward, giving the T boats an initial bow salvo of 10 fish. That was six in the bow tubes, plus two external bow tubes in the casing directly above the normal tubes and the two amidships externals.

Between the wars the French experimented with destroyer style rotating tubes on the decks of their larger "cruiser" submarines.

Today, computer aided aiming systems would make stern tubes as easy to use as bow tubes but the stern tubes would seriously interfere with modern streamlining.