Early patrols

Her first patrol took U-564 from Kiel to Brest in occupied France, spending a total of 41 days at sea. The patrol brought a number of successes; on 27 June Suhren came across convoy HX 133. He damaged the Norwegian tanker Kongsgaard and sank the Dutch Maasdam and the British Malaya II that day. He had one further success on that patrol, sinking the Icelandic merchantman Hekla on 29 June. U-564 put into Brest on 27 July, having sunk three merchant ships for 18,678 gross register tons (GRT), and damaged another for 9,467 GRT.^[4]

She sailed again from Brest on 16 August, heading into the Atlantic. She came across convoy OG-71 and sank the Irish Conlara and the British tug Empire Oak on 22 August. She sank an escort the following day, HMS Zinnia. U-564 returned to Brest on 27 August after 12 days at sea, having sunk three ships for 2,587 GRT. She sailed again on 16 September, this time encountering convoy HG-75 on 24 October. She sank three British merchantmen that day, Alhama, Ariosto and Carsbreck.^[4] U-564 was attacked later in the evening, by a bomb from an aircraft and later by an escort with depth charges. She escaped damage however, and returned to port at Lorient on 1 November having spent 47 days at sea and sunk three ships for 1,687 and 900 tons.^[4]

U-564 relocated to La Pallice in early 1942, and sailed from there on 18 January. She sank the Canadian tanker Victolite 260 nautical miles (480 km; 300 mi) northwest of Bermuda on 11 February 1942, and damaged the British tanker Opalia, although not severely (her deck gun firing 83 rounds, but only scoring three hits), on 16 February, before returning to Brest on 6 March, after 48 days on patrol with 11,410 GRT sunk and 6,195 GRT damaged.^[4]

Off the American coast

U-564 sailed from Brest on 4 April 1942, to cross the Atlantic and prey on shipping off the North American coast, including Florida. She was in position in early May and on 3 May, secured her first success, sinking the British Ocean Venus. On the 4 May, she damaged the British Eclipse, and on 5 May she damaged the American Delisle. On 8 May she sank the American merchantman Ohian, the following day she sank the Panamanian tanker Lubrafol. Her final success in American waters was to sink the Mexican tanker Potrero del Llano. U-564 arrived back in Brest on 6 June, having spent 64 days at sea and sunk four ships, for 24,390 GRT, and damaged two ships, for 13,245 GRT.^[4]

U-564 repeated the exercise on her next patrol, departing Brest on 6 July to operate off the coast of South America. Whilst outward-bound across the Atlantic, Suhren came across convoy OS-34 near the Azores, and on 19 July sank the British merchant Empire Hawksbill, and damaged the Lavington Court (sank 1 August whilst under tow back to the UK). Operating off the northern South America coast, he sank the SS British Consul and the Empire Cloud west of Grenada on 19 August and on the 30th, she sank the Norwegian tanker Vardaas north of Scarborough. U-564 arrived back in Brest on 18 September after 72 days on patrol, having sunk five ships for 32,181 GRT.^[4]

Fiedler takes charge

This was Suhren's last patrol as commander of U-564. He left on 1 October to become an instructor, Oberleutnant zur See Hans Fiedler took command.^[4] He took the boat on two war patrols in 1943 but failed to hit any enemy ships. On one of these sorties events took a dramatic turn when the U-boat lost a crewman, Fähnrich zur See (Ensign) Heinrich Fuerhake. U-564 was transferred to operate out of Bordeaux in April 1943. She left the French port city for the final time on 9 June with four other outbound U-boats, U-185, U-358, U-634 and U-653.^[4] A Royal Air Force Short Sunderland spotted the boats and attacked them off Cape Finisterre at 18.59 hours on 13 June. The aircraft targeted U-564 and dropped its bombs, but was shot down by anti-aircraft fire, killing all 11 of the crew. U-564 had sustained heavy damage and turned back, escorted by U-185.^[4]

Wolfpacks

U-564 took part in six wolfpacks, namely:

• Brandenburg (16 – 19 September 1941)
• Breslau (2 – 29 October 1941)
• Natter (2 – 8 November 1942)
• Westwall (8 – 16 December 1942)
• Seeteufel (21 – 30 March 1943)
• Löwenherz (1 – 10 April 1943)