I don't think he gave the actual speed, but Beach did say that they weren't going fast enough to hold the bow down with the planes (the periscope was up, so TRIGGER was probably doing two knots or less). This was on 10 June 1943, when she fired all six bow tubes at HIYO, probably scoring four hits. HIYO didn't sink, but was put out of action for the next year. (Possibly pointing out, also, the difference between a properly trained crew with lots of damage control drills behind them and a relatively untrained crew and inadequate damage control skills and systems--in a proper state of training, and with all systems working properly, SHINANO shouldn't have sunk.)

I don't think the designers actually thought in terms of "what do you do to maintain trim if you fire all six tubes in one salvo." Other than attacking a carrier or a battleship, it just wasn't all that likely anyone would do it. Two or three fish would normally be sufficient for most targets.

VADM James Calvert, in his book, mentioned that different methods applied to different vessels. Destroyers usually salvo fired their torpedoes at fairly long range; submarines tended to be more like sharpshooters, carefully aiming their torpedoes, and using no more than were absolutely necessary to obtain results.

On one patrol Mush Morton caught hell for firing single torpedoes, all of which, it was presumed, either missed or failed to detonate (this was just after the magnetic exploders were deactivated, but before the contact exploders were fixed), and was strongly encouraged to used two or three torpedo salvos. This was also the first patrol in WAHOO under Morton without Dick O'Kane on the periscope during attacks, so maybe the torpedoes actually DID miss.

J.T. McDaniel