S-class submarines exposed a gap between Soviet output and confidence

The Soviet Union had built submarines almost continuously since 1927, yet the S class reflects dissatisfaction with the performance of domestic technology. Earlier programs included a six-boat class built between 1927 and 1929, of which four were lost in the Second World War, and a later eighty-eight-boat production effort. S1, S2, and S3 used at least some German-supplied machinery, with engines and batteries identified among the imports. Later boats substituted domestic machinery made to similar specifications. Their Soviet diesels provided somewhat higher speed but were non-reversible, so the substitution changed operating characteristics as well as the supplier. The program shows foreign acquisition alongside an established domestic submarine industry whose output did not remove doubts about its equipment.