The limits of uncrewed submarine resupply

Would uncrewed submarines make effective underwater supply boats for operational submarines?

Only in limited cases; submerged docking and weapons transfer are difficult, vulnerable, and costly enough that a submarine tender may offer better value.

Uncrewed submarines could act as modern milk cows for deployed boats, but the transfer system would be a major engineering constraint. A useful system would need to rendezvous and transfer stores while both vessels remained submerged, because surfacing defeats much of the operational advantage. Torpedoes are the hardest requirement: a receiving submarine would need a safe docking or moon-pool arrangement and machinery to move heavy weapons into its magazine. Neutral or hostile powers could also interfere with expendable supply craft while denying deliberate participation in the conflict. The capability might suit rare circumstances, but the added interfaces could raise the cost of every submarine enough to reduce fleet numbers, making a next-generation tender a more attractive investment. For the nuclear-submarine operators most likely to afford this system, torpedo replenishment is a more pressing problem than supplying propulsion fuel.