Commander Michael Grant Goodenough RN joined Admiralty Plans Division on 28 August 1939. Within barely a week, Britain had declared war on Germany and Winston Churchill had become First Lord of the Admiralty, returning to the position he had been forced to relinquish in 1915.In October 1939, having served for a few weeks at the Admiralty, Michael Goodenough bought a large, soft-back foolscap notebook in which he started a diary that he kept until June 1941. The original manuscript is held by the Goodenough family. This transcript was prepared in 2020 by his eldest son, Sir Anthony Goodenough (born in 1941, a month after the diary ends). Sir Anthony’s brother Simon (born in 1945) contributed to this work. The diary has been edited to remove most family material as well as a few personal remarks on colleagues.