Enigma machine

Sub-Lieutenant David E. Balme, R.N. Photo credit: The Telegraph

Enigma’s Mysteries Revealed

by Thomas Sanger • Thomas C. Sanger • Leave a Comment

Nearly two years after the start of World War II, the British Royal Navy for the first time put a boarding party onto a crippled German submarine. On May 9, 1942, 20-year-old sub-lieutenant David Balme led a party of nine sailors onto U-110, not knowing if the boat had been booby-trapped and half expecting scuttling charges to detonate at any moment.

Balme and his men had been sent across from H.M.S. Bulldog by her captain, Commander Joe Baker-Cresswell, with orders to gather up signal books and any other useful materials they might find (see blog post “Lemp’s Fatal Mistake, Aug. 30, 2018). Balme was the first man into the submarine, and when he was certain the boat had been abandoned, he called for the rest of the men to join him in the U-boat’s control room.

“The lights were still on and everything was lying about just as if one had arrived at someone’s house after breakfast, before they had had time to make beds, etc., coats were thrown around, bunks half made,” he later remembered. “There was complete silence in the U-boat except for the continual thud of our own depth charges [in pursuit of a second U-boat]…a most unpleasant and frightening noise.”

He told the men to ignore anything that was obviously casual reading material and to take whatever else appeared to be of interest. Speed was of the essence because U-110 was sinking and Balme was still concerned about explosive charges. Complicating matters was the fact that none of the men read German.

At one point, a sailor came out of the U-boat’s radio room and told Balme, “There’s something rather interesting I want to show you.” In the cramped radio room, Balme was shown a typewriter-like device screwed to the table. He could see that pressing one key on the machine caused a different letter to light up on a display. Balme told the sailor to unscrew it and send it up with the rest of the material being gathered. The young sub-lieutenant had no way of knowing that his party had just recovered the first working model of the German naval Enigma machine, a top-secret prize British Intelligence had coveted since the start of the war.

As the day wore on and the submarine remained afloat, Balme became less concerned about scuttling charges or the boat’s quick demise. At one point, Bulldog sent over sandwiches and a small boat to replace the one that had smashed itself on the U-110’s deck. He did worry, however, when Bulldog was called away on a U-boat sighting and a dense fog settled on the ocean.

“There was I, with my boarding party aboard U-110 in the middle of the Atlantic, alone with no ships in sight and with the wind and sea gradually increasing,” Balme recalled. Fortunately, Baker-Cresswell’s dead-reckoning navigation skills brought Bulldog back to the crippled submarine before nightfall, and the treasure trove of materials, including the Enigma machine and its codebooks, were transferred to the British destroyer.

By day’s end, Bulldog took U-110 under tow in hopes of delivering her to Iceland for careful inspection by British submarine experts. The next day, however, the U-boat sank en route. By then, the submarine’s capture and its trove of materials had been given a top-secret designation with the code name “Primrose.” Great effort went into limiting the number of people made aware of Primrose, and the capture was kept secret for several decades after the war.

U-110’s sinking may have been a blessing in disguise. Had the boat been towed to Iceland, it is entirely possible that local German spies would have relayed its capture to German authorities. German naval commanders would have assumed their encrypted communications could be compromised and they would have made changes to the Enigma machine and its codes much sooner than was actually the case. Even after the Germans made modifications in an effort to restore the naval Enigma’s integrity, insights gained by British intelligence from the materials taken from U-110 helped reduce code-breaking to a matter of hours or days instead or weeks.

At least one naval historian went so far as to characterize Operation Primrose on a scale commensurate with the outcomes of the Battle of Midway in the Pacific and the Battle of Stalingrad in Europe – not a bad day’s work for a Royal Navy convoy escort group and a junior naval officer barely out of his teens.

German trawler Munchen is captured by a British destroyer. Photo credit: Warcovers website

Sea Battles Turn Tide of Events for Enigma Codebreakers

by Thomas Sanger • Thomas C. Sanger • Leave a Comment

After a brief lull in the Battle of the Atlantic during January, 1941, German U-boats began to sink increasing numbers of Allied ships: 47 ships in February and 50 ships in March. But in March, a naval engagement off the coast of Norway was about to produce a valuable prize for Britain’s Bletchley Park code breakers. (See my blog, “Decoding Enigma: Success and Setback,” June 18, 2018.)

During a March 4th British commando raid, a Royal Navy destroyer engaged in a brief gun battle that left a German trawler disabled and burning. While the Germans abandoned their crippled ship, a three-man boarding party went across to the trawler. The leader of the party, Lt. Sir Marshall Warmington, broke into a locked desk in the captain’s quarters and found a wooden box containing two small, ratcheted wheels. Although he hadn’t been briefed on the German Navy’s Enigma coding device, Warmington thought the box looked intriguing. He retrieved it and some unimportant looking papers.

The papers turned out to be a bonanza for the Bletchley cryptanalysts. They contained Enigma settings for February, helping the analysts read several encoded German Navy messages from the previous month. With the help of these “cribs,” the analysts were able to construct the German bi-gram (two-letter) table used in transmitting the Enigma settings for individual messages. Even with this advantage, however, the decoding process still took weeks to complete.

To speed up the process, the Royal Navy quietly began putting together plans to capture a U-boat or other German naval vessel in hopes of obtaining more current Enigma codebooks. Thus far in the war, however, the Royal Navy had realized only limited success in sinking U-boats, let alone capturing one.

At this point, a radio traffic analyst at Bletchley Park proposed an inspired solution. In looking through the decrypted messages, Harry Hinsley saw that the Germans were sending trawlers to the seas north of Iceland to observe and report the weather conditions back to naval headquarters. Hinsley believed these lonely ships were equipped with Enigma machines and codebooks in order to send and receive certain secret messages. If such a ship suddenly came under attack, he reasoned, the crew might think to throw overboard their Enigma device and current codebooks, but likely would be too panicked to take the time to retrieve and destroy the next month’s codes, locked away for safekeeping.

The plan worked exactly as envisioned. On the afternoon of May 7, 1941, a Royal Navy destroyer opened fire as it raced toward the German trawler München. Moments after the trawler’s crew were picked up by the British, a boarding party from the destroyer climbed aboard the München, and this time they were joined by a London-based Intelligence officer who had been told what to look for and where he was likely to find it.

As expected, München’s crew had disposed of the Enigma machine and current codebooks, but not the codebooks for June. Three days later, the June codes were delivered to cryptanalysts at Bletchley, a gift that would allow them to read the German Navy’s June radio traffic within hours of it being sent.

Yet even as this operation was being hailed, another trove of information was falling into Royal Navy hands, courtesy of the same U-boat commander whose attack on the passenger ship Athenia had begun the Battle of the Atlantic 20 months earlier. More about that dramatic action in our next blog.

Photo caption: Dr. Arthur Scherbius, German electrical engineer who developed the Enigma machine. Photo credit: Alchetron

The Evolution of Enigma

by Thomas Sanger • Thomas C. Sanger • Leave a Comment

In my last blog (“The Mystery of Enigma,” May 1, 2018), we explored the ingenious design of the German Enigma machine. The encryption device provided so many possible permutations for each letter in a message that it seemed impossible for Enigma’s code to be broken.

Despite Enigma’s close association with World War II, the device actually was developed at the end of World War I. Arthur Scherbius, the German engineer who created the Enigma, sought to interest the German navy and the Foreign Office in his newly patented design in 1919, but both turned him down.

Scherbius formed a company and exhibited his first machine in 1924 at an international gathering of postal officials. That first model, marketed under the brand name “Enigma,” incorporated an actual typewriter, weighed just over 100 lbs., and lacked many of the refinements of later models.
By 1927 Scherbius designed a machine that was lighter and more portable. The new model proved popular, and the company sold Enigmas to commercial markets in Europe, Scandinavia, the United States, and Japan. At about the same time, the German navy and army acquired upgraded Enigmas that included the plugboard design, a feature not available on commercial models.
Over the next decade, the German military models underwent further tweaks and upgrades to become even more inscrutable than their commercial cousins. For example, the army’s Enigma version incorporated a fourth wheel, while the navy continued to use the three-wheel design but introduced two additional wheels that could be interchanged with any of the three original wheels.

Beginning in the late 1920’s military intelligence operations in Britain, France and Poland set about trying to break the German military Enigma code. They had no success until late 1931 when an executive in the German Defense Ministry began spying for the French and provided a copy of the Enigma instruction manual as well as three-letter codes used to set up the machines.

This material was passed by the French to the Poles, who were further along with their decryption efforts owing to the Poles’ greater affinity with German engineering and their proximity to a re-arming German state. Using the spy’s information, Polish mathematicians succeeded in working out the internal wiring of each of the Enigma wheels, and in 1933 Polish intelligence built several prototype Enigmas and began to read German military communications. The Poles, however, did not inform the French or British of their success.

Every day each branch of the German military set their Enigma machines to a pre-arranged master setting which included the order of the wheels, the setting of the initial letter on each wheel, and the plugboard connections. From this arrangement, the sender transmitted a new random three-letter code for the initial wheel settings then adjusted the machine’s wheels to the new settings and typed the message. The receiver decoded the initial three letters, re-set the receiving machine’s wheels accordingly and decoded the message that followed.

The Poles used an arrangement of six prototype Enigmas to determine the wheel positions of the German machines each day. To read individual messages, they relied on the German practice of repeating the random three-letter setting at the beginning of each transmission.
The Polish cryptographers were able to keep up with most German modifications, reading military communications for nearly five years. On the eve of World War II the Germans made physical changes to their Enigma machines and changed code-sending practices, leaving Polish intelligence unable to “eavesdrop” on the German military. The battle to solve Enigma shifted to a new front, as we’ll see in our next blog.