In the summer of 1940, Britain stood alone. France had fallen, invasion seemed possible, and Winston Churchill faced a grave question: what should be done about the powerful French fleet?

Fearing it might fall under German control, Britain launched Operation Catapult. At Mers el Kébir on 3 July 1940, the Royal Navy opened fire on its former ally, killing nearly 1,300 French sailors in one of the war's most painful and controversial decisions.

For this episode, I am joined by Edward Abel Smith, author of 'A Hateful Decision', which tells the full story of this dramatic moment through new research and eyewitness accounts.