Only for the selected tube. I generally set speed and depth then hit Q (open outer door) then W (switch to next tube) and repeat until all the tubes I intend to shoot are set and open when the target is still 5000+ yards away. I also set the AOB to 80 (or whatever it looks like it will be at the moment of firing) when they're still 3000 yards or so, since you won't have time to do it at closer range - the AOB changes slowly at long range but too quickly to keep up with at close range.
Personally I use the auto open = false hack;
http://www.subsim.com/radioroom/show...00&postcount=3
So I don't waste torpedoes, if the outer door isn't already open the tube won't fire.