On retirement, Quinlan became Director of the
Ditchley Foundation, holding the position until 1999. In 2001, he became Chairman of
The Tablet Trust, publisher of the Catholic newspaper
The Tablet. He was one of the world's foremost experts in
deterrence theory, contributing to debate and books in this field. He also wrote his own book on this matter shortly before his death. His contributions were recognised by
Gordon Brown, the Prime Minister of the United Kingdom, in a speech given on 17 March 2009. Historian of government
Peter Hennessy called him the
leading in-house defence intellectual MOD has possessed since World War II. He died on 26 February 2009. ==Honours==