Before the Normandy landings, the Allies created fictitious armies, radio traffic and double-agent reports suggesting that the main invasion would strike Pas-de-Calais. From headquarters in Britain, Operation Fortitude exploited German expectations and confidence in selected agents. German units remained near Calais even after troops landed in Normandy.

Fortitude turned fictional characters, invented formations and scripted radio conversations into instruments of war. Its methods later influenced spy novels, memoirs and drama concerned with unstable identity, authorship and the dangerous power of believable stories.