A research group investigating the Voynich Manuscript Operational 1962-3, and involving William F Friedman and others. Their work has been investigated by Jim Reeds.

The material is in the William F. Friedman Collection at the George Marshall Library, Lexington, VA (Wikipedia page [1]): the website is [2].

A partial transcript is available - there is a note that the transcript is almost illegiblesee [3].

In Craig Bauer's 'The History and Mystery of the World's Greatest Ciphers from Ancient Egypt to Online Secret Societies' p 558 there is reference to William Friedman et al Printout of partial transcription, Second Study Group ca 1963 WFF 1609.3 and 'Correspondence with RCA Corp. about activities of "Second Study Group," 1963, WFF 1609.4 (visible via Google Books).

See also First Study Group