Two days before thousands of Allied troops stormed the French port of Dieppe on August 19, 1942, the Daily Telegraph crossword offered the clue French port, six letters, and MI5 launched an investigation into the compiler. It was a fluke, but it captures the chaos surrounding Operation Jubilee, a raid that ended with a 68 percent casualty rate among the mostly Canadian assault force. Drawing on declassified military records and recent research on covert commando units, this episode asks whether Dieppe was a hard-learned lesson that made D-Day possible or a reckless slaughter driven by ego and faulty intelligence.

The episode lays out the competing pressures that produced the raid, from Stalin's demands for a second front and restless Canadian troops who booed their own prime minister to an RAF Fighter Command hunting for a decisive air batt ...