From the longer Wikipedia article 
Brigadier John Hessell Tiltman MC (25 May 1894 – 10 August 1982) was a British Army officer who worked in intelligence, often at or with the Government Code and Cypher School (GC&CS) starting in the 1920s. His intelligence work was largely connected with cryptography, and he showed exceptional skill at cryptanalysis. His work in association with Bill Tutte  on the cryptanalysis of the Lorenz cipher , the German teleprinter cipher, called "Tunny" at Bletchley Park, led to successful attack methods. It was to exploit those methods that Colossus , the first digital programmable electronic computer, was designed and built.
In 1951 Tiltman met William F Friedman, one of the leading scholars involved in the attempt to decipher the mysterious Voynich manuscript. Tiltman undertook an analysis of the ancient manuscript himself, and then in the 1970s he assigned the NSA cryptanalyst Mary D'Imperio to take over the Voynich cryptanalysis, when Friedman's health began to fail. D'Imperio's work became the book The Voynich Manuscript: An Elegant Enigma, and is now considered one of the standard reference works on the Voynich Manuscript. Tiltman wrote the Foreword to this book.
An article on his breaking the Lorenz Code is here .