External torpedo storage

[Max Horton]

I'm new to SH3, and using GWX, which I'm finding extremely enjoyable. I have one question, though (possibly dopey) concerning external torpedo storage in Type-IX subs: how do you get torpedoes from the external storage to load into the sub's tubes? I ask because I was on a cruise in a Type-IX, and having expended all of my internal torpedoes, did not seem to be able to replenish my tubes using the externally stored torps. Is this meant to happen automatically, in which case, are there certain criteria to be satisfied for it to occur, or is there some way in which I can manually load?

Thanks.