In July 1942, the merchant sailors of Convoy PQ-17 watched their entire naval escort turn and speed away, followed by a single radioed word: scatter. This episode reconstructs the Anglo-American operation to deliver Lend-Lease tanks, aircraft, and supplies to the Soviet Union through the Arctic, where perpetual summer daylight, freezing spray, and thermal layers that blinded sonar made cargo ships sitting ducks. We examine why summer sailing was still safer than winter routes forced close to German-occupied Norway.

The disaster turned on intelligence. Bletchley Park was reading German Enigma traffic, but the German B-Dienst had broken British Naval Cipher No. 3 and Finnish intelligence had handed over the convoy’s itinerary. Fearing the battleship Tirpitz was at sea, First Sea Lord Admiral Dudley Pound overrode his own intelligence officer’s judgment and ordered the convoy to scatter. The Tirpitz had not sailed. Twenty-four of 35 merchant ships were sunk, 153 seamen died, and hundreds of tanks and aircraft went to the bottom.

• Lend-Lease quotas of 400 aircraft and 500 tanks a month and why the Soviets could not carry them
• Lieutenant Commander Norman Denning’s warning about negative intelligence that Pound ignored
• The three escalating orders issued between 21:11 and 21:36 on July 4, 1942
• Lieutenant Leo Gradwell hiding HMS Ayrshire and three merchant ships in the ice under white bedsheets
• The fallout with Stalin, Admiral Ernest King, and the suspension of Arctic convoys for the rest of the summer