Thor (HSK 4, 10 or Raider E) was a German auxiliary cruiser of the Kriegsmarine in the Second World War, intended for service as a commerce raider. The ship was named after the Germanic deity Thor, known to the Kriegsmarine as and to the British as Raider E.

Thor began its first cruise on 6 June 1940 with Captain Otto Kähler and returned via the Bay of Biscay on 23 April 1941, having spent 329 days at sea and sank or taken as prize twelve ships of 96,547 GRT. After a refit, Thor began its second cruise with a new captain Günther Gumprich. After colliding with and sinking a Swedish ore carrier and a period in dock for repairs, Thor sailed on 30 November 1941.

Thor docked at Yokohama on 9 October 1942, having sunk or captured ten ships of 55,587 GRT on a voyage of 328 days. On 30 November, the tanker docked next to Thor and soon afterwards began to explode and set Thor on fire. Gumbrich rallied the survivors and took on the raider Michel with a composite crew.

Michel sank another three ships, then while hunting in the Pacific, Michel was torpedoed by . Michel sank with the loss of Gumbrich and 262 men. Some survivors were taken back to Germany by , a blockade-runner that was mistakenly sunk near the Canary Islands by with only one survivor.

Background Commerce raiding Auxiliary cruisers (raiders) were, for a small outlay in crews and material, a means of oceanic operations for the that could force the Allies into considerable counter-measures, divert ships and aircraft and inflict considerable attrition on merchant ships through sinking or capture. The (Naval War Staff) used the experience of the First World War to convert ships into disguised auxiliary cruisers, with fairly heavy gun- and torpedo-armament and from 1942 radar. High cruising speeds of and long endurance were necessary. SKL planned to use wireless to direct raiders to different areas and to give a running commentary on circumstances by passing on wireless intelligence.

SKL strategy was to tie down and disrupt Allied sea operations, rather than obtain a high number of sinkings at the risk of the loss of raiders. Ship captains were directed to make surprise appearances, to force the Allies to divert many ships for trade protection. Tankers and supply ships were to fuel, provision and supply the raiders by exploiting the inability of the Admiralty to maintain a continuous watch over the oceans. Merchant ships, were to be taken by preventing them from sending distress signals. Raiders were to transfer captured merchant crews to the supply ships.

Each ship would need a crew of 284 men, six -guns, four 20 mm anti-aircraft guns, four torpedo tubes, provision for 400 mines, two seaplanes and some ships carried a light, fast E-boat for mining harbour entrances and surprise night attacks against merchant ships. The ships needed to be at sea for yearlong cruises of . The first raider was to sail in November 1939 but it took until 31 March 1940 before it sailed and July before the first wave had completed their departures. By March 1941 the seven raiders in action had sunk or taken 80 ships of (GRT).

B-Dienst

The German (, Observation Service) of the (MND, Naval Intelligence Service) had broken several Admiralty codes and cyphers by 1939, which were used to help Kriegsmarine ships elude British forces and provide opportunities for surprise attacks. In 1941, read signals from the Commander in Chief Western Approaches informing convoys of areas patrolled by U-boats, enabling the submarines to move into "safe" zones. broke Naval Cypher No 3 in February 1942 and by March was reading up to 80 per cent of the traffic, which continued until 15 December 1943. By coincidence, the British could not read the Shark cypher and had no information to send in Cypher No 3 which might compromise Ultra.

Prelude

Santa Cruz/Thor The cargo ship Santa Cruz (, ) was long, with a beam of , a draught of and a speed of . The ship was built by Deutsche Werft, Hamburg, (DWH) in 1938 and was owned and operated by the Oldenburg Portuguese Line (OPDR) Hamburg. In the winter of 1939–1940 the requisitioned the ship and had DWH convert it into an auxiliary warship by DWH. The ship was commissioned as the (commerce raider) Thor on 15 March 1940.

Operational Intelligence Centre Pre-war thinking at the Admiralty under-estimated the threat from U-boats and expected that the principal weapon of the would be the commerce raider. Between the wars the Admiralty and the Royal Air Force had never agreed about the control of maritime aircraft or grasped the role and effectiveness of aircraft over the seas, their strategy and tactics or their design and armament. In 1939 the Germans could only reach the high seas via the Scotland–Iceland gap or the Denmark Strait between Iceland and Greenland. The Admiralty revived the Northern Patrol to intercept Blockade runners and detect the passage of German s (pocket battleships) that had been built as commerce raiders. In late 1940 the Operational Intelligence Centre created a sub-section to concentrate on armed merchant raiders to collect information that a raider was at sea based on ship disappearances, survivor reports on the appearances of raiders, their tactics and armaments, the presence of mines and the analysis of times and distances to infer the number of raiders.

As the presence of a raider was established it received a code letter, beginning with Raider A. It was discovered that the Germans named the ships and gave them a number (Thor [Raider E] was 10). From May 1941 a supplement of the Weekly Intelligence Report listed raiders, their size, speed, armament, captain, drawings or photographs their characteristics, tactics and a digest of their cruises. The wireless signal QQQQ was established for attacks by merchant raiders to go with RRR for attack by any ship and SSS for submarine attack. In May 1941 the cruiser intercepted a distress message from a tanker in the Indian Ocean that led to the sinking of Raider F ( ) that had been at sea for close to a year, sank or took as Prize of war 17 ships and 11 whalers of 136,000 GRT. The seven raiders at sea between April 1940 and November 1941 sank or took as prizes 87 ships of over 600,000 GRT.

First cruise June 1940

Thor (Captain Otto Kähler) began its first cruise on 6 June 1940, altered to look like the Russian freighter Orsk from Odessa. The ship was escorted into the North Sea by destroyers, minesweepers and aircraft. The British and French were evacuating troops from Harstad in the north of Norway, with a lot of ships in the area. As the ship sailed northwards, the weather deteriorated, enveloping the ship in fog and snow, despite the midnight sun and it passed unseen. Thor/Orsk passed through the Denmark Strait and reached the North Atlantic on 16 June. On 22 June, Kähler reported to Berlin that Thor was west of the Azores and had changed disguise to the neutral Vir a Jugoslavian ship from Split.

July 1940

On 1 July, Thor/Vir, met the 9,289 GRT Dutch cargo ship Kertosono, which was carrying a cargo of petrol, timber, asphalt and agricultural machinery. Kähler decided to send it under a prize crew to Lorient in France, where it arrived on 12 July. On 7 July, just south of the Equator, Thor encountered Delambre, a British 7,030 GRT freighter carrying hides and cotton to Britain. Delambre turned away leading to a stern chase and when Thor had closed the range to about several broadsides, were fired, the third of which hit Delambre and stopped it. A boarding party took the crew of 44 and a passenger prisoner and scuttled the ship with demolition charges.

Two days later on 9 July, Thor intercepted the Belgian freighter Bruges, bound for Freetown with of wheat. Bruges was scuttled and its crew of 44 was taken aboard Thor. On 14 July, Thor stopped Gracefield, another British freighter, carrying of wheat and bran from Montevideo. The 36-man crew was taken prisoner and two torpedoes were fired at the ship, one hit and the other circled the ship until it ran out of fuel; the ship was sunk by gunfire.

On 16 July Thor spotted a large plume of smoke from the British freighter Wendover (5,489 GRT) carrying coal to Buenos Aires. Thor approached by hiding in the smoke plume and opened fire without warning, as Wendover was seen to have two guns at the stern. Wendover was hit by several shells and set on fire. The wireless operator began sending "QQQQ" and a crewman was seen running towards the guns at the stern. Another salvo hit the wireless cabin, killed the operator and with the fires spreading, the captain stopped the ship. Kahler sent a boarding party over that set demolition charges. Wendover capsized when the charges detonated, then was finished off by gunfire. Two members of the crew were killed in the attack, 37 were taken prisoner, two of whom were mortally wounded and died on board Thor, being buried at sea.

The Dutch freighter Tela, carrying of grain to Britain was intercepted on 17 July, Thor firing a shot across its bow and it stopped without sending distress signals. The crew of 33 men abandoned ship and were taken aboard Thor, the ship being sunk with demolition charges. In just over two weeks Thor had sunk six ships of 35,201 GRT and taken 194 prisoners. For ten days Thor stayed in the south Atlantic off the Brazilian coast. The prisoners were roused at for roll call at then after breakfast, shifts of 60–70 came on deck for sun, exercise and fresh air.

Alcantara

On 28 July, Thor encountered a grey-painted ship that was hard to identify and eavesdropped on a wireless message reporting Thor and calling for help. The ship was the armed merchant cruiser HMS Alcantara, with a main armament of eight BL 6-inch Mk XII naval guns (150 mm) two 3-inch guns and sundry anti-aircraft guns. Admiral Henry Harwood, the commander of the South American Division, North America and West Indies Station, had reacted to the number of overdue ships and Admiralty signals intelligence that raiders were operating in the South Atlantic. Using reports of survivors, Harwood inferred that a raider was moving southwards and sent Alcantara to search for it. At about on 28 July, off Argentina, on a clear day with a calm sea, lookouts on Alcantara spotted a strange ship that turned away at high speed, arousing the suspicions of the captain, James Ingham.

Alcantara was capable of , faster than Thor and at about when the range was about Kähler decided to try to inflict enough damage on Alcantara to escape. Thor gained three early hits on Alcantara, one between the bridge and funnel, a second aft and a third on the waterline that caused flooding in the engine room, forcing Alcantara to reduce speed. Alacantara replied with its 6-inch guns but was out-ranged by about and facing the sun, making it harder to aim. After the fire control system was damaged, the gunners had to fire independently. Despite the difficulties, Thor was hit several times, one shell passing unexploded through the hull and damaging a shell hoist; another shell hit the boat deck and put the torpedo fire control system out of action. Using its reserve W/T, Alcantara sent "Enemy approximately 8,000 tons, speed 19 knots, armament four 5.9-inch guns". Thor turned away from Alcantara, that had lost speed due to the shell-damage and instead of fighting on, Thor escaped under a smokescreen and changed disguise once out of sight.

August–September 1940