[Aktungbby]

Originally Posted by Jimbuna

1941 British intelligence at Bletchley Park breaks German spy codes after capturing Enigma machines aboard the weather ship Müenchen.

Indeed the capture was two days prior to the code capture of U-110; which often gets all of the credit in movies and TV... after all, weatherships and trawlers are mundane! A useful but short lived victory; Moreover Operation Claymore in Norwegian waters on March 4 1941 had resulted in the capture of the German armed- trawler Krebs recovering its Enigma equipment and codes...the most significant outcome of the raid. The Brits severely damaged the trawler, and killed 14 German sailors, took another 25 prisoner, While the attack boosted British public morale temporarily, the Enigma machine still eluded the British military. The commander of the Krebs, Lieutenant Hans Kupfinger, threw it overboard before he was killed in the raid, but the Brits were able to recover documents that gave clues to the Enigma’s workings. The capture of a set of rotor wheels for an Enigma cypher machine and its code books enabled British intelligence to piece together enough of the German coding system to track German naval activity for about five weeks. German naval codes now read at Bletchley Park, provided the intelligence needed to allow Allied convoys to avoid U-boat concentrations.

The BritishcryptologistHarry Hinsley, then working at Bletchley Park realised at the end of April 1941 that the German weather ships, usually isolated and unprotected trawlers, were using the same Enigma code books as were being used on the heavily armed U Boats. The trawlers, which were transmitting weather reports to the Germans, were in turn being sent naval Enigma messages.Although the weather ships did not transmit enciphered weather reports on Enigma machines, they still needed to have one of the machines on board if they were to decode the Enigma signals transmitted to them. Hinsley realised that if the code books could be captured from one of these vulnerable trawlers, the naval Enigma system could be broken, with British intelligence able to decipher messages to U-boats and discover their locations. The problem remained that if the navy were to attempt to capture one of the weatherships, the German crew would have time to throw their current Enigma settings into the sea before they were boarded. Hinsley instead reasoned that the following month's Enigma settings would be locked in a safe aboard the ship, and could be overlooked if the Germans were forced to hastily abandon ship. On being informed, the Admiralty despatched seven destroyers and cruisers to the northeast of Iceland at the beginning of May 1941. The target was München, one of the weather ships operating in the area. In the course of the raid, the weather ship, and the Enigma settings for June 1941 were captured. As with Krebs, the Müenchen's captain had thrown the Enigma coding machine over the side as HMS Somali approached. ( One may properly conclude that trawler captains were more Enigma security minded than U-boat Kaleuns??!!) ... but he too had left the coding tables for the months of May and June on his desk. These were duly collected by Captain Haines. Some of Muenchen's crew were taken on board Somali, but most were accommodated in Edinburgh. Somali escorted the captured vessel to Scapa. Nestor took Captain Haines back to Scapa at speed and he was immediately flown to London with the vital documents. As a result, naval Enigma messages transmitted during June 1941 could be quickly deciphered. However: Halfway through June 1941 the Germans replaced the bigram tables used in Enigma. This would have resulted in a codebreaking blackout unless further settings could be captured. Hinsley and the Admiralty were concerned that capturing another weather ship might alert the Germans to their vulnerability and cause them to immediately alter them again. It was eventually decided to take the risk and on 25 June 1941 four warships, the light cruiser HMS Nigeria and the destroyersHMS Tartar, HMS Jupiter and HMS Bedouin, were despatched from Scapa Flow to capture the codebooks from Lauenburg, another weather ship operating north of Iceland, which Hinsley had selected...on June 28 the converted trawler Lauenburg was captured in similar fashion-the recovered Enigma material allowed further understanding of the Enigma codes and resulted in faster decoding of encrypted messages, as well as providing an up-to-date set of codes.

Lauenburg sunk by British taskforce. wiki et al http://www.iankitching.me.uk/family/colin/ww2/operation-eb.htm It's amazing to me that: 'twixt the Krebs, U110, Müenchen and the Lauenburg, all taken in a four-month period, German thought did not turn to a complete alteration of their severely compromised code system??!! The more so, as Müenchen had radioed an "enemy in sight" report that enabled yet another targeted weathership to escape: it is likely that the other ship had hastened eastwards on picking up the message.