This section includes much of Bacon's most important fuel cell correspondence and covers an exceptionally extended period. Although Bacon kept correspondence files for a small number of named individuals such as the Cambridge University authority on metallic corrosion U.R. Evans and fuel cell associates T.M. Fry and R.G.H. Watson, most of the correspondence presented in this section was kept in three major chronological sequences: 'fuel cell' correspondence 1933-1991, 'personal' correspondence, 1952-1991, and 'miscellaneous' correspondence, 1953-1975. The 'personal' and 'miscellaneous' correspondence sequences also relate to Bacon's fuel cell interests.

For long periods Bacon wrote most of his letters by hand. Nevertheless, even when writing by hand he made carbon copies and thus his correspondence is unusually complete. Bacon's correspondence files also often include notes of telephone calls and meetings including those with visitors to his private home.