Hi dragoneer2 and welcome to the forum.
As UKönig says if you have used
all torpedoes on board you can only replenish at:
1. Your home base port (with all crew, upgrade & re-supply options available)
2. Another friendly base (limited options)
3. At a German supply ship or U-tanker (also limited)
If you still have reserve torpedoes aboard but don't know how to load them let us know and we can help. Reloading external reserves can be a bit tricky...
What type of boat are you driving?
KH