How long were you assigned to a submarine in WW2?

There was a fair amount of variation here, but it appears that a man would typically be assigned to the same boat for about 15 to 18 months of combat. The Pampanito’s war patrols covered a period of 13 months and just 30 of her original crew made all six patrols. That would be consistent with about 15% of the crew rotating off after each patrol.

In peacetime, men and women are typically assigned to the same ship for two to three years. Again, there can be a fair amount of variation.