Pages 201 through 204,
"In 2010, Krag, citing German sources, discussed the technical development of these two missiles and a number of subsequent derivations in the Soviet Union. It is therefore not necessary to duplicate Krag's account other than to mention that tests with the Soviet versions of the Wasserfall, designated R-101, and the Schmetterling, designated R-102, continued in the Soviet Union until 1951 and 1950 respectively, and formed the basis for further experimental designs of surface-to-air guided missile systems which eventually led to the first and second operational Soviet systems, the S-25 and S-75."
"According to one source, the design of the guidance and control system of the S-25 was also assisted by German expertise."