Why S-boats could not replace German destroyers

Could Germany's S-boats make up for the shortcomings of its destroyer force?

No. S-boats were effective in their own role but could not provide ocean-going fleet escort, and Germany needed several times more destroyers to support its planned heavy ships.

The estimate assigns roughly a destroyer flotilla to each capital ship and half a flotilla to each cruiser. On that logic, Germany should have ordered about sixteen ships in each of the 1934, 1934A, and 1936 groups, producing at least forty-eight destroyers by the outbreak of war. Losing eleven ships around Narvik would then have been painful but recoverable. Starting with twenty-two instead reduced the force to eleven, below even its peacetime operational needs. Force structure, rather than the quality of S-boats, was the decisive limitation.