A Nimrod could carry 6 or 9 torpedoes in racks of 3.
For a single prosecution it was likely that only 2 would be dropped. After the first wad dropped it would take a finite time to relocate the target. Clearly you might get a one shot kill. You might also get a second chance quickly.
Your chance of a third drop, especially on a second submarine, would be slim.
Most torpedoes would be expended on close support with urgent attacks used more for deterrence.
It follows therefore that rearming, if time was of the essence, could be deferred if at least 4 weapons remained. The critical turn round would be fuel and continuous.
And crew wise, until you ran out of crews, should not be a problem. Read Hackett' s book WW 3.