'EC' (ii) was a British naval undertaking undertaken as successor to 'EB' for the capture of the German weather ship Lauenburg specifically for the seizure of her Enigma encryption machine and associated codebooks (25/30 June 1941).
The 344-ton Lauenburg was a converted trawler used in the early years of World War II for the provision of weather reports in support of German maritime operations, especially those of U-boats, and the vessel’s capture, before she was deliberately sunk on 28 June, allowed the Royal Navy to acquire important German codebooks and parts of an Enigma machine, and came after the German use of such vessels had been identified as a weakness that could be exploited to break the Enigma code.
Built in 1938 as a fishing trawler, Lauenburg was named for a town on the Elbe river, and operated from Geestemünde before she was acquired from her owner, H. Bischoff & Co. of Bremen, by the Kriegsmarine in 1940. Carrying a crew of 19 to 21 men, Lauenburg was adapted for the carriage of a team of eight meteorologists and their equipment, which included an Enigma machine used not to transmit the weather data but to receive Kriegsmarine orders. The revised vessel entered naval service in November 1940 with fuel and other supplies sufficient to undertake patrols of two months or more in northern waters.
The British cryptologist Harry Hinsley, then working at the Government Code & Cipher School at Bletchley Park, Bedfordshire, had realised at the end of April 1941 that the German weather reconnaissance force, usually operating in isolated waters with largely unprotected adapted trawlers, carried the same Enigma codebooks as were being used by U-boats. Although the weather ships did not transmit enciphered weather reports on their 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 reached the conclusion that if the code books could be captured from one or preferably more than one of these vulnerable trawlers without the Kriegsmarine concluding that its naval code system had thereby been compromised, the naval Enigma system could be broken. This would allow Bletchley Park’s cryptologists to decipher messages to U-boats and thereby discover their locations so that important convoys could be rerouted to avoid their patrol lines.
The main tactical problem was how to capture one or more of the weather ships before the Germans were able to use the inevitable delay between the appearance of British warships and the arrival of their boarding parties to jettison their Enigma machines and associated papers into the sea. Careful analysis of the Germans' probable method of operation suggested to Hinsley that while the current month’s papers might be kept in the Enigma room and be readily jettisonable with the Enigma machine, the books and other papers associated with the following month’s operations would be kept locked in a safe and might therefore be overlooked by the Germans who, even if they did decide also to throw these overboard, might not have the time to do so.
The first British target was München, one of the weather ships operating to the north of Iceland, and 'EB' was proposed by Hinsley and proved successful in capturing the vessel on 7 May. The raid also netted the Enigma settings for June 1941. As a result, the German naval Enigma messages transmitted during June 1941 could be quickly deciphered. Halfway through June 1941, however, the Germans replaced the code tables used in their Enigma system, which would have led to a codebreaking blackout unless further settings could be captured. Hinsley proposed seizure of another weather ship, in this instance the 344-ton Lauenburg, which operated from Trondheim in German-occupied Norway, but the Admiralty was initially concerned that the British capture of two weather ships within six weeks might alert the Germans to their code traffic vulnerability and cause them to make an immediate change in their settings. The importance of continued Bletchley Park capacity to decrypt Enigma traffic prevailed, however, and the Admiralty authorised 'EC', with planning and command entrusted to Rear Admiral H. M. Burrough, commanding the 10th Cruiser Squadron of Admiral Sir John Tovey’s Home Fleet.
The force which departed Scapa Flow on 25 June for 'EC' comprised the light cruiser Nigeria and the destroyers Bedouin, Jupiter and Tartar. The British ships refuelled at at Skaalefiord in the Færoe islands group and then headed to the north.
At about 19.00 on 28 June one of Tartar's lookouts sighted Lauenburg off Jan Mayen island, and Tartar opened fire with the object not of hitting the ship but of causing her crew to panic and abandon ship. Lauenburg's crew quickly abandoned the ship in two lifeboats, and just minutes later Tartar steamed alongside and despatched a boarding party to seized Lauenburg. The boarding party seized a large quantity of German material that was swiftly transferred to Tartar before the British ships sank Lauenburg with gunfire.
All the British ships reached Scapa Flow once more on 30 June.
The recovered material was rushed back to the UK and was very rapidly assessed to allow further understanding of the Enigma codes and the faster decryption of intercepted German messages.