Much of the work done by the BNF during the 1939–45 period was of vital use for the defence industry.  This especially included solving many of the corrosion problems of seawater cooled condenser tubes and tube plates that had resulted in many ships being unserviceable and significant improvements in corrosion resistant alloys for seawater pumps and pipe fittings.  No work was ever carried out on active materials for nuclear weapons.  Some consultancy work was undertaken on paperwork for new designs.
There has been much publicity about Melita Norwood  (née Sirnis) who joined the BNF in 1932 as a clerk, was eventually promoted to secretary and retired 1972.  As secretary to a Research Superintendent she had access to the papers prepared at the BNF for presentation to the research committees and some contractors.  Some of these she chose to copy to Russian intelligence. This information was made use of by them and did occasionally result in one of their research organisations publishing development work on non-ferrous metals similar to and sooner than the BNF in Britain.