Flooding tubes

[Nisgeis]

Here'e the procedure for flooding a tube:

http://hnsa.org/doc/fleetsub/tubes/chap9.htm

It doesn't seem like it's a long job, but not that quick either, so probably a few minutes? Something you'd want to do shortly before firing. I believe captains tried to avoid having the tubes flooded for too long, as the pressure affected torpedoes badly.