German U-boat standardization and innovation

Did Germany innovate with submarines in World War II or mass-produce a few established types?

It did both: the Type VII family was produced in great numbers, while later innovation drew heavily on concepts the Dutch had already developed.

Germany relied heavily on repeated Type VII variants to create fleet numbers. That production programme still allowed incremental changes within a familiar design. Innovation continued alongside it. Some important later ideas, however, adapted work already undertaken in the Netherlands rather than emerging wholly from German development.