On the morning of 9 May 1941, in the North Atlantic south of Iceland, the German submarine U-110 attacked convoy OB 318 and was promptly blasted to the surface by depth charges from the escorts. Her commander, Fritz-Julius Lemp — the man who had sunk the liner Athenia on the first day of the war — ordered his crew to abandon ship, believing she was going down. She didn't. From the destroyer HMS Bulldog, Commander Joe Baker-Cresswell saw the U-boat wallowing and sent across a boarding party under a 20-year-old sub-lieutenant, David Balme, who climbed down the conning tower ladder into a silent, listing submarine, half-expecting scuttling charges. His party formed a human chain and passed up charts, codebooks and a curious typewriter-like machine that a telegraphist recognised as interesting: an Enigma cipher machine, with its settings and current key sheets. Lemp did not survive; U-110 sank under tow the next day — from the security point of view, conveniently. The Royal Navy called the affair Operation Primrose and buried it in secrecy so deep that even the ship's company was sworn to silence.
Hollywood later rearranged the story. The 2000 film U-571 depicted American submariners capturing an Enigma in 1942, years before the United States' real Enigma capture took place, provoking complaints in the House of Commons; the film-makers added an end caption acknowledging the real Royal Navy captures. The irony is that no single "pinch" won the code war — Bletchley Park was fed by a whole series of planned thefts.
Pinches by design
The historian-in-the-making Harry Hinsley, then a young Bletchley analyst, noticed that German weather ships in the Atlantic carried the same cipher materials as warships but almost no guns. The trawler Krebs, wrecked during the Lofoten Islands raid of March 1941, had already yielded key material; in May and June 1941 the weather ships München and Lauenburg were deliberately hunted down and boarded, each surrendering current key tables that let Bletchley read naval Enigma nearly in real time. Each pinch was stage-managed to look like chance, because the entire enterprise depended on Germany never suspecting its ciphers were compromised.
Then the lights went out. In February 1942 the Atlantic U-boats added a fourth rotor to their Enigma machines — the net Bletchley called Shark — and for ten months the codebreakers were effectively blind while sinkings soared. Bletchley's frustration was such that its senior codebreakers had already written directly to Churchill pleading for resources, drawing his famous "Action this day" instruction. The blackout ended off Port Said on 30 October 1942, when destroyers including HMS Petard forced U-559 to the surface after a hunt lasting some ten hours. Lieutenant Tony Fasson and Able Seaman Colin Grazier stripped and swam to the sinking submarine, hauling out the Short Weather Cipher and Short Signal Book; they were still inside when she went down, and both received the George Cross posthumously. Tommy Brown, a sixteen-year-old NAAFI canteen assistant who had lied about his age to join up, made repeated trips to the hatch, survived, and became the youngest recipient of the George Medal in military service. The captured documents broke Shark within weeks — a turning point in the Battle of the Atlantic.
Credit where due
One more correction Hollywood and legend both need: Enigma was first broken not at Bletchley but in Poland. The mathematicians Marian Rejewski, Jerzy Różycki and Henryk Zygalski of the Polish Cipher Bureau reconstructed the military Enigma from 1932, and in July 1939, at a meeting near Pyry outside Warsaw, handed Britain and France working replicas and their methods — weeks before the invasion that destroyed their country. Bletchley then industrialised the attack on a scale the Poles could never fund: Alan Turing designed the bombe, Gordon Welchman's diagonal board transformed its power, and by the war's end some two hundred of the machines were grinding through rotor settings around the clock. The whole enterprise — codenamed Ultra — stayed secret until F. W. Winterbotham's book The Ultra Secret appeared in 1974, which is why men like Balme, Fasson, Grazier and the Polish trio spent decades unthanked. Historians still debate how much time Ultra bought — Hinsley himself suggested the war was shortened by around two years — but the accounting is done in convoys that arrived, and in the strange arithmetic by which a few sodden codebooks outweighed fleets.
Quiz nuggets
- U-110 and its Enigma machine were captured on 9 May 1941 by a boarding party from HMS Bulldog led by Sub-Lieutenant David Balme.
- U-110's commander Fritz-Julius Lemp had sunk the liner Athenia on the first day of the war.
- Tony Fasson and Colin Grazier of HMS Petard drowned retrieving codebooks from U-559 in 1942 and received posthumous George Crosses; 16-year-old Tommy Brown won the George Medal.
- Polish mathematicians Rejewski, Różycki and Zygalski first broke Enigma and handed replicas to the Allies at Pyry in July 1939.
- The Ultra secret held until F. W. Winterbotham's 1974 book revealed it.