Stationed in Europe during World War II and in Vienna during Austria's occupation by the allies, he became a noted expert on the recent history of the country, especially on the lives of the last ruling Habsburgs, the psychological and political turbulence of the interwar period, and the Anschluss.
[2] On vacation in Europe shortly before the outbreak of World War II, Brook-Shepherd noticed that many of Nazi Germany's new autobahnen led directly to France.
He worked as a secretary for the Joint Intelligence Committee; his office was the former sitting room of Empress Zita in Schönbrunn Palace, a place that had long fascinated him.
[6][7] Brook-Shepherd's two most influential books on Austrian history are Dollfuss, his eponymous 1961 biography of the interwar Austrofascist dictator, and Anschluss, his 1963 account of the incorporation of Austria into the German Reich.
[3] Anschluss was compared favorably with earlier studies on the subject by Ulrich Eichstädt and Jürgen Gehl; Brook-Shepherd received praise for his "intimate, personal knowledge of places and people" and for his "psychological insight linked with critical detachment".
[8][4][9] While Gehl described the Anschluss mainly as the result of Hermann Göring's forceful personality and Hitler's vacillating indecision,[10] Brook-Shepherd took a more systemic view.
Starting his account in 1931, earlier than other historians at the time, he emphasized the roles of impersonal social forces as well as happenstance; he also ascribed comparatively complex sets of mutually contradictory personal and ideological goals to many of the actors.
[8] Brook-Shepherd's second area of interest was the recent history of British and Soviet intelligence; his work on those subjects was characterized by his unique network of contacts and access to archives.