This was the British retrospective cover designation for the ‘EB’ capture of U-110 (9 May 1941).
A number of highly secret cipher documents were recovered from the U-boat, and the undertaking’s significance led to the retrospective allocation of the codename ‘Primrose’ (ii).
Commissioned on 21 November 1940 under the command of Kapitänleutnant Fritz-Julius Lemp, U-110 completed two war patrols, sinking three ships (10,149 tons) and damaging two others (8,675 tons). On 23 March 1941 the boat’s 105-mm (4.13-in) deck gun exploded as a it was being fired, wounding three men, and on 9 May of the same year the boat was captured and later sunk.
U-110 and U-201 were attacking convoy OB.318 in the North Atlantic in the area to the south of Iceland when the failure of torpedo launch distracted Lemp, and U-110 was located by the sonar equipment of the corvette Aubrietia, which then depth-charged the boat. U-110 only just survived the attack, but was badly damaged and helpless. After a second depth-charge attack, the boat surfaced and Lemp ordered his crew to abandon ship. As the crew mustered on the U-boat’s deck they came under fire from the destroyer Bulldog and escort destroyer Broadway, several of the German sailors being killed or drowning after falling in the water as a result of their wounds. The British had believed that the Germans were about to open fire with the U-boat’s deck gun, and ceased fire when they realised that the U-boat was being abandoned and the crew preparing to surrender.
The escort commander, Captain J. Baker-Cresswell in Bulldog, had initially made to ram the U-boat but then recognised the opportunity for its capture, and hove to before strafing the submarine. Broadway also closed in, intending to prevent U-110 submerging and in the process suffering incidental damage.
Lemp had assumed that his U-boat, with its vents open, would sink and had therefore ordered the radio operator to leave the codebooks and Enigma enciphering machine and get out. Lemp then realised that U-110 was not sinking and attempted to swim back to the boat and destroy the secret material, but was never seen again. Including Lemp, 15 men were killed in the action and 32 captured.
Bulldog’s crew stripped U-110 of everything portable, including her secret documents and Enigma cipher machine, and then took the boat in tow back toward the UK, but the sank en route to Scapa Flow.
The documents captured from the U-boat helped the codebreaking teams at Bletchley Park to break the German navy’s Reservehandverfahren (reserve hand cipher).