The Mediterranean U-boat Campaign lasted from about 21 September 1941 to 19 September 1944 during the Second World War. Malta was an active British base strategically located near supply routes from Europe to North Africa. Axis supply convoys across the Mediterranean Sea suffered severe losses, which in turn threatened the fighting ability of the Axis armies in North Africa. The Allies were able to keep their North African armies supplied. The Kriegsmarine tried to isolate Malta but later it concentrated its U-boat operations on disrupting Allied landing operations in southern Europe.

Some 60 German U-boats made the hazardous passage into the Mediterranean Sea from 1941; however, none successfully returned to the Atlantic.Paterson (2007) pp. 19, 182 Karl Dönitz, the Commander-in-Chief, U-boats, Befehlshaber der Unterseeboote (BdU) was always reluctant to send his boats into the Mittelmeer but he recognised that natural bottlenecks such as the Straits of Gibraltar were more likely to result in shipping being found and attacked than relying on finding it in the vast Atlantic Ocean.

The U-boats were sent to assist the Italians, although many were attacked in the Strait of Gibraltar and nine were sunk while attempting the passage and ten more were damaged. The Mediterranean is a clear and calm body of water which made escape more difficult for the U-boats.Paterson, 11th photo caption, between pages 74 and 75 The Axis failed in their objective.

Prior Experience The Kriegsmarine had acquired some knowledge of the area. Dönitz was an officer aboard which had been sunk in the region in World War I.Paterson, p. 6 U-boats had also served in the Spanish Civil War. The Republicans, with twelve submarines, opposed the Nationalists, who had none; the presence of German U-boats was most welcome. The first two vessels, U-33 and U-34, under the codename Training Exercise Ursula, left Wilhelmshaven on 20 November 1936. Both submarines sailed down the English Channel and slipped into the Mediterranean on the night of 27 November. They were soon in action, U-34 fired a single torpedo at a Republican destroyer in the evening of 1 December. The projectile missed, impacting on rocks. The boat, under Leutnant zur See Harald Grosse, tried again on 5 and 8 December, with an equal lack of success. U-33 fared no better; her commander was frustrated by the absence of target identification or defensive movement of his intended victims. Only one vessel was sunk by the U-boats, the Republican submarine C-3, which was attacked by U-34 on 12 December.

The early years By October 1939, Dönitz had decided to use three longer-range boats to intercept the first Allied convoys of the war. , and were to rendezvous southwest of Ireland before attempting to force the Straits and attack the convoys in the Mediterranean. Things went quickly wrong, U-25 was diverted to a convoy south-west of Lisbon. After an abortive torpedo attack on a steamer on 31 October, Viktor Schütze, U-25s commander, surfaced and proceeded to sink his target with fire from his deck gun. This course of action caused a crack in a vital part of the submarine, obliging the boat to return to Germany. U-53 ran low on fuel after shadowing a convoy in the Bay of Biscay and was also forced to return. U-26, was compelled by a combination of unsuitable weather, searchlights and British anti-submarine patrols, to abandon an attempt to lay mines near Gibraltar harbour. The boat sailed through the Straits on the surface and claimed but a solitary ship sunk in the Mediterranean. This 'sinking' was not confirmed by post-war analysis.

U-26 headed back through the Straits, arriving in Wilhelmshaven on 5 December 1939; the only U-boat to enter and leave the Mediterranean in the war.Paterson, pp. 19, 182. This mission was summed-up in the BdU Kriegstagebuch (KTB) War Diary,

It was a mistake to send U-25, U-26 and U-53 into the Mediterranean. U-25 had to return before she ever got there, U-53 did not get through and U-26 hardly encountered any shipping worth mentioning. This patrol shows all the disadvantages of a long outward passage.|KTBPaterson, p. 20

Many attacks mentioned were gun actions or ramming, particularly at the eastern end of the Mediterranean. This was because the potential target was "unworthy or [a] difficult torpedo target".Paterson, 23rd photo caption between pages 74 and 75

Afrika Korps The 23rd U-boat Flotilla was established in September 1941 to intercept coastal shipping supplying Allied forces in the Siege of Tobruk. U-boats patrolled the eastern Mediterranean from the 23rd flotilla base on Salamis Island in Greece. On 7 December, control of the 23rd Flotilla was transferred from Kernével to The Commander in Chief in the South (Oberbefehlshaber Süd, OB Süd) Albert Kesselring. Additional bases were established in Pula in Croatia and La Spezia in northern Italy as more U-boats were ordered to the Mediterranean, until focus shifted to the western Atlantic through the Second Happy Time.Blair (1996) pp.395-404 passed Gibraltar on 21 September 1941.Blair (1996) pp.735–736 passed Gibraltar on 26 September 1941, and sank on 27 November, the 3,059-ton Shuntien of convoy TA 5 on 23 December, and the 2,487-ton Warszawa of convoy AT 6 on 26 December. passed Gibraltar on 27 September 1941, sank the 1,208-ton Samos and the 758-ton Pass of Balmaha on 17 October. passed Gibraltar on 30 September, destroyed a 372-ton British landing craft on 10 October, and sank on 25 November 1941.Blair (1996) pp.399&736 passed Gibraltar on 3 October, sank two 372-ton British landing craft on 12 October, and sank the 1,587-ton Volo of convoy ME 8 before being sunk by convoy escort on 28 December 1941.Blair (1996) pp.403, 735–736 passed Gibraltar on 5 October, damaged on 21 October, and was sunk on 23 December 1941 by Royal Navy destroyers. passed Gibraltar on 11 November 1941. passed Gibraltar on 12 November and sank on 13 November 1941.Blair (1996) pp.396–397, 736 was sunk near Gibraltar on 16 November 1941 by . passed Gibraltar on 16 November 1941. passed Gibraltar on 24 November 1941 and damaged the 3,560-ton Myriel on 13 December. passed Gibraltar on 26 November, sank the 4,032-ton Fjord on 2 December, then sank on 15 December, and was sunk on 16 December 1941 by the .Blair (1996) pp. 400, 736 passed Gibraltar on 27 November 1941 and sank the 4,274-ton Grelhead on 2 December. was torpedoed by the Dutch submarine O 21 while passing Gibraltar on 28 November 1941. passed Gibraltar on 29 November 1941, sank the 1,595-ton Saint Denis on 9 December, and sank the 6,557-ton Varlaam Avanesov on 19 December. passed Gibraltar on 8 December 1941. passed Gibraltar on 9 December 1941. passed Gibraltar on 9 December 1941 and sank the Spanish ship Badalona on 13 December. sank the trawler HMS Lady Shirley and the patrol yacht HMS Rosabelle while passing Gibraltar on 10 December 1941Blair (1996) pp. 403, 716–719 and was torpedoed by on 12 January 1942.Taylor (1966) p.124 passed Gibraltar on 10 December 1941 and sank on 24 December passed Gibraltar on 15 December 1941. passed Gibraltar on 16 December 1941 and damaged on 12 January 1942. passed Gibraltar on 18 December 1941. passed Gibraltar on 18 December 1941 and sank the 5,289-ton Hellen on 21 December. was sunk by Fairey Swordfish from 812 Naval Air Squadron while passing Gibraltar on 21 December 1941. passed Gibraltar on 21 December 1941. passed Gibraltar on 23 December 1941 and was sunk by aircraft on 9 January 1942. passed Gibraltar on 14 January. passed Gibraltar on 15 January 1942

Second Happy Time La Spezia became headquarters when the Mediterranean U-boats were reorganized as the 29th U-boat Flotilla in May 1942. No more U-boats were assigned to the Mediterranean from mid-January to early October 1942 as opportunities along the east coast of North America seemed more productive while the Afrika Korps was successfully advancing on Egypt. The 29th flotilla focused on convoys supplying Malta and British forces on the Egyptian coast. For sustained operations, U-boats spent approximately one-third of the time on patrol stations, one-third in transit to and from base for routine provisioning and refueling, and one-third undergoing major overhaul or battle repair. 29th flotilla target strength of twenty U-boats enabled a routine patrol strength of three U-boats from Salamis in the eastern Mediterranean, and three from La Spezia in the western Mediterranean. Loss of U-372 and U-568 in twelve-hour sustained attacks demonstrated vulnerability of independent U-boat patrols to a team of destroyers which could hunt a submerged U-boat to exhaustion of air and battery power, rather than moving on after a few attacks.Blair (1996) pp.645–654 sank on 11 August 1942. was sunk on 2 May 1942 by aircraft and destroyers. sank on 12 June. U-77 then sank sailing ships Vassiliki on 22 July, Toufic El Rahman on 24 July, Fany on 30 July, and Saint Simon on 1 August. U-77 continued patrolling the coast of Cyprus, Palestine and Lebanon damaging Adnan and sinking Ezzet on 6 August, Kharouf on 10 August and Daniel on 16 August 1942. sank the 6,018-ton Caspia, the French trawler Viking, and sailing ships Bab el Faraq and Farouh el Kher on 16 April 1942. U-81 sank sailing ships Hefz el Rahman on 19 April, Aziza and the El Saadiah on 22 April, and then 2,073-ton Havre of convoy AT 49 on 10 June 1942. damaged the 2,590-ton Crista on 17 March 1942, sank the 100-ton Esther and the 231-ton Said on 8 June, the 175-ton Typhoon on 9 June, the Q-ship HMS Farouk on 13 June, and the 5,875-ton Princess Marguerite on 17 August 1942. sank the 1,755-ton Memas and the 1,433-ton Zealand from convoy Metril on 28 June 1942, and sank the 786-ton Marilyse Moller on 1 July. sank on 17 January 1942Blair (1996) pp.553–554 and sank after striking a mine off Salamis on 12 March 1942.Taylor (1966) p.116 sank the 2,623-ton Slavol on 26 March 1942, and sank on 16 June 1942. shelled the Beirut electric power station in April 1942.

sank on 30 June 1942, and was hunted to exhaustion on 3 August 1942. sank the 1,376-ton Hero on 6 July 1942, sank the 87-ton Amina and the 176-ton Ikbal on 30 July, and damaged the 6,288-ton Empire Kumari of convoy LW 38 on 26 August. She also sank the 558-ton Arnon, the 38-ton Miriam and the 108-ton Salina on 3 September. She then sank the 113-ton Turkian on 6 September 1942. sank the trawler HMS Sotra on 29 January 1942, she then sank the 4,216-ton Eocene of convoy AT 46 on 20 May, and damaged LCT-119 on 20 June 1942. damaged the hospital ship Somersetshire on 7 April 1942. sank the 4,681-ton Athene and damaged the 5,917-ton Brambleleaf of convoy AT 49 on 10 June 1942. planted a minefield at the mouth of the Suez Canal, sinking the 6,692-ton Mount Olympus, and damaging the 5,062-ton Hav and the 4,043-ton Fred. damaged the 3,359-ton Adinda on 24 July 1942. sank on 11 March 1942 and the 1,361-ton Kirkland of convoy TA 36 on 23 April. was hunted to exhaustion on 28 May 1942. was interned in Spain following bomb damage on 1 May 1942. sank on 20 March 1942, sank on 26 March and was sunk on 2 June 1942 by 815 Naval Air Squadron.

Allied invasion of North Africa

More U-boats were assigned to the 29th flotilla when improved anti-submarine warfare (ASW) measures along the east coast of North America ended the Second Happy Time. When a Short Sunderland found U-559, the aircraft summoned five destroyers able to maintain contact and drop 150 depth charges over ten hours, until the submarine attempted to sneak away on the surface at night. Waiting destroyers open fire as soon as the U-boat surfaced and the U-boat crew abandoned ship. The Royal Navy boarded the sinking U-boat and recovered German code documents before U-559 sank.Blair (1998) pp.81–103