No message, it just doesn't fire. Lesser of evils to me, because I hit the fire button and nothing happens, at least I don't waste a torpedo. Hit the Q key, count to 5, then take another bearing on the target before shooting. Even if it takes a whole minute to start over and you got a less than perfect angle and firing solution, you'll still get a much higher percentage of hits than that useless automatic door opener gives you.
Good habit to get into, if the target is in visual range, cycle through the tubes and open all the outer doors. Check the little message window, if you see "closing tube 3" hit the Q key again to get "opening tube 3" before hitting W to cycle to the next tube.