A modern submarine's crew knowledge outlasts its weapons

If a Virginia- or Seawolf-class submarine went back in time, what would matter most: propulsion, sonar, weapons, or crew knowledge?

Crew knowledge is the most immediately useful and sustainable asset once modern ammunition and support become unavailable.

A nuclear plant could provide power and limited mobility without a contemporary support base. Modern sonar and other sensors would remain valuable only while their specialized parts stayed serviceable. Weapons would eventually run out or become impossible for the earlier industrial system to replace. The crew's engineering, tactical, and organizational knowledge is therefore the most transferable advantage because it can influence many ships and institutions after the submarine's unique stores are exhausted.