SM U-66 was the lead ship of the Type U-66 submarines or U-boats for the Imperial German Navy () during World War I. The submarine had been laid down in Kiel in November 1913 as U-7, the lead ship of the U-7 class for the Austro-Hungarian Navy ( or ). They became convinced after the outbreak of war in August 1914 that none of these submarines could be delivered to the Adriatic via Gibraltar, and sold the entire class, including U-7, to the German Imperial Navy in November 1914.
Under German control, the class became known as the U-66 type and the boats were renumbered; U-7 became U-66, and all were redesigned and reconstructed to German specifications. U-66 was launched in April 1915 and commissioned in July. As completed, she displaced when surfaced and submerged. The boat was long and was armed with five torpedo tubes and a deck gun.
As a part of the Baltic and IV Flotillas, U-66 sank 25 ships with a combined gross register tonnage of 73,847 in six war patrols. The U-boat also torpedoed and damaged the British cruiser in August 1916. U-66 left Emden on her seventh patrol on 2 September 1917 for operations in the North Channel. The following day the U-boat reported her position in the North Sea but neither she nor any of her 40-man crew were ever heard from again. A postwar German study offered no explanation for U-66s loss, although British records suggest that she may have struck a mine in the Dogger Bank area.
Design and construction After the Austro-Hungarian Navy had competitively evaluated three foreign submarine designs, it selected the Germaniawerft 506d design, also known as the Type UD, for its new U-7 class of five submarines.Gardiner, p. 340. The Navy ordered five boats on 1 February 1913.Gardiner, p. 343.
The U-7 class was seen by the Austro-Hungarian Navy as an improved version of its U-3 class, which was also a Germaniawerft design.The U-3-class submarines, however, were less than half the displacement and nearly shorter than the U-7 design. See: Gardiner, pp. 342–43. As designed for the Austro-Hungarian Navy, the boats were to displace on the surface and while submerged. The double-hulled boats were to be long overall with a beam of and a draft of . The Austrian specifications called for two shafts with twin diesel engines ( total) for surface running at up to , and twin electric motors ( total) for a maximum of when submerged. The boats were designed with five torpedo tubes; four located in the bow, one in the stern. The boats' armament was to also include a single /26 deck gun.
U-7 and sister boat were both laid down on 1 November 1913, the first two boats of the class begun.Helgason, Guðmundur. "WWI U-boats: U 66", "U 67", "U 68", "U 69", "U 70". U-Boat War in World War I. Uboat.net. Retrieved 9 December 2008. Their construction was scheduled for completion within 29 to 33 months, but neither U-7 nor any of her sister boats were complete when World War I began in August 1914. Because the boats were under construction at Kiel on the Baltic Sea, the Austrians became convinced that it would be impossible to take delivery: the boats would need to be transferred into the Mediterranean past Gibraltar, a British territory.The Austro-Hungarian Navy's Germaniawerft-built U-3 class boats had been towed from Kiel to Pola via Gibraltar in 1909. See: Sieche, p. 19. As a result, U-7 and her four sisters were sold to the Imperial German Navy on 28 November 1914.Gardiner, p. 177.In April 1915, just five months later, the German successfully entered the Mediterranean through the Strait of Gibraltar, proving that delivery could have been possible after all. See: Gardiner, p. 343.
U-7 was renumbered by the Germans as U-66 when her class was redesignated as the Type U-66. The Imperial German Navy had the submarines redesigned and reconstructed to German standards, increasing the surface and submerged displacements by , respectively. The torpedo load was increased by a third, from 9 to 12, and the deck gun size was upgraded from the size originally specified to SK L/30.
Early career U-66 was launched on 22 April 1915. On 23 July, SM U-66 was commissioned into the Imperial German Navy under the command of Kapitänleutnant (Kptlt.) Thorwald von Bothmer, a 31-year-old, thirteen-year veteran of the Imperial German Navy. U-66 was assigned to the Baltic Flotilla () on 17 October.Tarrant, p. 34.
In late September, the British submarine flotilla in the Baltic began a submarine offensive against German ships, intending to deny free passage of cargo, especially iron ore, from neutral Sweden to Germany.Halpern, p. 202. In A Naval History of World War I, author Paul G. Halpern reports on part of the German response, which was an experiment involving U-66. The U-boat was towed behind an "innocent-looking vessel" and connected to the host ship by a telephone line in addition to the towline. U-66 was able to cast off at a moment's notice to attack an enemy submarine. Halpern does not report on any encounters by U-66, nor does he provide any insight into the overall effectiveness of the plan.Halpern, p. 204. U-66 was not credited with the sinking of any vessels of any kind during this time. On 15 January 1916, she was transferred from the Baltic Flotilla into the IV Flotilla (), where she joined her sister boats and .Both of U-66s remaining sister boats, and , were attached to the IV Flotilla by early March, and for just under three weeks (until was sunk), all five of the Type U 66 boats were in the same unit. See; Tarrant, p. 30 (for sinking of U-68), and p. 34 (for Flotilla membership).
Second German offensive Germany began its second submarine offensive against shipping the month after U-66 joined the IV Flotilla. As in the first submarine offensive, U-boats were sent independently around Scotland to patrol the Irish Sea and the western entrance to the English Channel.Tarrant, pp. 27–28. The first reported activity of U-66 during this campaign reveals that she sank her first ship on 5 April 1916. On that date she was in the vicinity of Fastnet Rock and came upon the 3,890-ton British refrigerated cargo ship Zent headed from Garston to Santa Marta in ballast. U-66 torpedoed Zent from Fastnet and sank the ship with the loss of 49 crewmen;Tennent, p. 74. the master and nine sailors were rescued and landed at Queenstown. Over the next two days, U-66 dispatched two French sailing vessels, the 151-ton Binicaise, and the 397-ton fishing smack Sainte Marie west of the Isles of Scilly.Details, location: Type of ship: On 8 April, von Bothmer and U-66 sank the Spanish-flagged Santanderino from Ushant. Santanderino, a 3,346-ton ship built in 1890, was sailing from Liverpool to Havana, and U-66 gave 15 minutes' notice for all the passengers and crew to abandon ship; four drowned during the evacuation. Santanderinos 36 survivors were rescued by a Danish steamer and landed at a port on the Bay of Biscay.
U-66 continued her attacks on merchant shipping on 9 April with the sinking of three ships, the British steamers Eastern City and Glenalmond and the Norwegian ship Sjolyst. The 4,341-ton Eastern City was sailing from Saint-Nazaire to Barry Roads in ballast when she was shelled by U-66 and sent to the bottom from Ushant;Tennent, p. 210. all of her crew survived and were landed by 11 April. U-66s next victim was the 2,888-ton Glenalmond sailing from Bilbao to Clyde laden with iron ore. Torpedoes from U-66 sank the ship north of Ushant,Tennent, p. 100. but all her crew were saved. The 20-year-old Norwegian steamer Sjolyst was sailing in ballast from Nantes to Manchester when U-66 sank her about two nautical miles (four kilometers) from where Glenalmond went down. Sjolysts master and entire crew were picked up by the British steamer Libra and landed at Cardiff.
U-66 finished out her busy month the next day by sinking one British and one Italian ship. U-66 sank the British steamer Margam Abbey southwest of the Lizard while the ship was en route from Bordeaux to Barry Roads in ballast. Margam Abbey, at 4,471 tons, was the largest ship sunk by U-66 to that time.Tennent, p. 237. The Italian freighter Unione was sailing with a load of coal from Clyde for Genoa when U-66 torpedoed her off Land's End. The sinking of Unione, with a tonnage of 2,367, raised U-66s tally for the month of April to nine ships with a combined tonnage of 22,848, all sunk in a six-day span. Near the end of April 1916, Admiral Reinhard Scheer, the new commander-in-chief of the High Seas Fleet (under which U-66s IV Flotilla operated), called off the merchant shipping offensive and ordered all boats at sea to return, and all boats in port to remain there.Tarrant, p. 30.
Grand Fleet ambushes In mid-May 1916, Scheer completed plans to draw out part of the British Grand Fleet.Gibson and Prendergast, p. 97. The German High Seas Fleet would sortie for a raid on Sunderland,Tarrant, p. 31. luring the British fleet across "'nests' of submarines and mine-fields". U-66 was one of nine U-boats that put out to sea beginning on 17 May to scout the central North Sea for signs of the British fleet. Completing five days of scouting, U-66, along with , , , sister boat , , and , took up position off the Firth of Forth on 23 May. The other two boats, and , were stationed off Pentland Firth, in position to attack the British fleet leaving Scapa Flow. All the boats were to remain on station until 1 June and await a coded message which would report the sailing of the British fleet. Unfortunately for the Germans, the British Admiralty had intelligence reports of the departure of the submarines which, coupled with an absence of attacks on shipping, aroused British suspicions.
A delayed departure of the German fleet for its sortie (which had been redirected to the Skagerrak) and the failure of five U-boats, including U-66, to receive the coded message warning of the British advance caused Scheer's anticipated ambush to be a "complete and disappointing failure".Tarrant, p. 32. Although she had not received the advance warning of the coded message, U-66 was one of the two ambush U-boats that actually saw parts of the British fleet. At 09:00 on 31 May, U-66 sent out a wireless report of eight battleships, light cruisers, and destroyers on a northerly course east of Kinnaird Head.Gibson and Prendergast, p. 99.The other U-boat that reported activity, , stationed off the Firth of Forth, had reported seeing two battleships, two cruisers and several destroyers headed in a southeasterly direction two hours earlier. U-66 was unable to make any attacks on the ships she reported due to the presence of screening vessels. The failure of the submarine ambush to sink any British capital ships allowed the full Grand Fleet to engage the numerically inferior High Seas Fleet in the Battle of Jutland, which took place 31 May – 1 June.Tarrant, pp. 32–33.
The next mention of U-66 in sources is on 11 August, when she sank Inverdruie, a 613-ton three-masted Norwegian bark. Inverdruie was carrying a load of pit props from Sandefjord to Hartlepool when she was sunk some east of Aberdeen.
Later in August, the Germans set up another ambush for the British fleet, when they drew up plans for another High Seas Fleet raid on Sunderland (as had been the original intention in May). The German fleet planned to depart late in the day on 18 August and shell military targets the next morning. U-66 was one of 24 U-boats that formed five lines () in the expected paths of any Grand Fleet sorties. Standlinie II, consisting of , , , U-66, and , formed a front off Flamborough Head. The other four Standlinie formed similar lines to the north and south; all were to be in place by 08:00 on 19 August. Once again, British intelligence had given warning of the impending attack and ambush, causing the Grand Fleet to sortie at 16:00 on 18 August, five hours before the German fleet sailed.Tarrant, p. 33.