My practice, in concession to real world limitations, has been to reload externals in a calm sea, boat stopped or moving very slowly, and obviously away from the enemy. If I have to crash dive because of a plane, I consider that torpedo "lost" for the duration of the patrol. In reality, a crew would cut it loose and dive away. It would take a few seconds or minutes to either dismantle or abandon the external winch used to load them. You could use that time to simulate the crew abandoning the torpedo and dismantling/abandoning the winch, and it would not be available again until you returned to port.
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