HSK THOR

HSK Thor: The German Merchant Raider in WWII Essay

The HSK Thor, also known as Schiff 10 or Raider E by the Allies, was a German auxiliary cruiser that operated as a commerce raider during World War II. Used by the Kriegsmarine to hunt Allied merchant shipping, the Thor embodied Germany’s effort to neutralize Allied naval superiority by targeting merchant ships with the use of disguises and long-range commerce-raiding missions. Purchased by the Kriegsmarine under the name Santa Cruz, a powerful yet ordinary-looking cargo ship was converted into an auxiliary cruiser and fitted with concealed weapons. The Thor’s two combat cruises from 1940 to 1942 resulted in 22 ships sunk or captured, with a total of over 150,000 gross register tons, making it one of the most successful German commerce raiders. This article will explore the design of HSK Thor, the characteristics that made her special, and her most important roles in battles and operations of World War II.

Design of the HSK Thor

Origins as a Merchant Vessel

The Thor was originally the cargo ship Santa Cruz. Built in 1938 by Deutsche Werft in Hamburg, Germany for the Oldenburg Portuguese Line, Santa Cruz was a relatively small freighter with a gross register tonnage of 3,862, a length of around 122 meters and a beam of 16.8 meters. It was powered by two diesel engines, with a maximum speed of 17 knots. A reliable and functional merchant vessel, Santa Cruz was a suitable candidate to be refitted by the Kriegsmarine into an auxiliary cruiser. Its profile as a medium-sized, unspectacular cargo ship made her an ideal masquerade for a commerce raider.

Conversion into a Merchant Raider

In the winter of 1939–1940, the Kriegsmarine bought Santa Cruz and had it refitted into an auxiliary cruiser at Deutsche Werft in Hamburg. Designated Handelsstörkreuzer 4 (HSK-4), the ship was commissioned in March 1940 as the Thor. A wide variety of weapons were installed for the Thor, but were all carefully camouflaged to keep the ship’s disguise as a regular merchant vessel. The Thor’s primary armament was six 15-centimeter guns, sourced from older Kriegsmarine warships. They were mounted on the broadside to allow them to attack, with three guns on the aft for stern chases. Secondary armament included one 6-centimeter gun, four 3.7-centimeter anti-tank guns and four 2-centimeter anti-aircraft guns, all of which were hidden behind false panels. The Thor was also equipped with four torpedo tubes, two on deck and two submerged. The cruiser was also fitted with an Arado 196 A-1 seaplane for reconnaissance purposes and carried several hundred sea mines. Powered by its diesel engines, the Thor had enough range to support her two long-range cruises in 1940 and 1941, but her smaller size limited her cargo capacity when compared to larger raiders like Kormoran.

Command of the Thor’s first and second cruises were given to Kapitän zur See (Captain at Sea) Otto Kähler and Kapitän zur See (Captain at Sea) Günther Gumprich respectively. During her first cruise, the Thor was disguised as various neutral ships including the Soviet Donau and Japanese merchant ships to approach her targets. During the ship’s second cruise, the Thor was refitted with a newer set of guns and equipped with a newer radar system.

What Made the Thor Special

Role in Commerce Raiding

Thor was one of nine German merchant raiders that were used by the Kriegsmarine in its efforts to prey on Allied merchant shipping, with the aim to neutralize the Allies’ dominance of the seas. The Kriegsmarine’s policy for its auxiliary cruisers was to operate for as long as possible without support from the main fleet, hunting and sinking ships far from German ports while its own supply ships would be used to resupply the raiders. It was a tactic the Kriegsmarine used as a means to counter its position of being outgunned and out-numbered by the combined naval power of the Allies. Thor’s smaller size made her less conspicuous than some of her larger counterparts. Combined with her disguise as an unassuming cargo ship and superior long-range weaponry, Thor was a large enough threat to easily overpower merchant ships and engage and disengage from armed merchant cruisers at will.

The Thor’s use of disguises as Allied or neutral ships also meant that the raider was able to move freely amongst the merchant traffic with less risk of being identified as a raider. The various neutral and Allied disguises Thor used were also able to obtain relevant information from the merchant vessels they passed, making for a better-informed commerce raider. For example, the Thor was able to pick up signals and reports of Kormoran from the ships it passed and had also received intelligence of the latter’s intended routes from merchantmen prior to the ships meeting in the Indian Ocean. It was a common practice for the Kriegsmarine to use German agents disguised as neutral sailors or passengers aboard prizes in order to gain information on Allied shipping activities and supply routes, and the Thor’s false identities and quick concealment of her armament allowed her to freely employ this strategy.

Gun Disguises and Tactical Engagement

Thor’s primary tactic was to pose as an innocent civilian ship to close in on her targets and then quickly reveal her true nature by lowering her whaling mask and revealing her true armament. An example of Thor’s engagement with armed merchant cruisers, which emphasized the element of surprise, was her battles with HMS Alcantara and HMS Carnarvon Castle. Both ships were armed merchant cruisers of over 20,000 gross register tons with a battery of 6-inch guns, making them a match for the Thor. Thor’s commander Kähler used deception tactics like slow reaction times to targets attempting to flee and direct attacks from her stern to lure them into engaging the raider in a head-to-head fight. Thor’s deception and disguise also allowed her to make attacks without fear of retaliation; several of the Thor’s victims, which included unarmed and smaller prize ships, never fired back at her because they were taken by surprise, and even large and armed vessels like the Alcantara and Carnarvon Castle were unable to counter Thor’s attack until it was too late.

Air and Reconnaissance Advantage

Thor’s use of disguises was further bolstered by her superior long-range reconnaissance, made possible by the ship’s Arado seaplane. Thor used the plane to spot and approach her targets and also to keep a lookout for warships, giving her the air advantage to better coordinate her commerce-raiding operations. Thor’s air advantage was exemplified when it was able to make a short-range attack on the lone American tanker Pan Virginia using its Arado to coordinate the attack and guide it into range. Her air advantage also helped Thor locate and support other Kriegsmarine forces in the area; her second cruise saw the Thor rendezvous with the Admiral Scheer and transfer crew for the raider’s prize ships, which she would have been hard-pressed to find without the help of her seaplane.

Versatility and Self-Sustainability

Thor’s diesel engines and cargo space also allowed her to carry the provisions needed for a long cruise without resupplying. This allowed the Thor to sustain her long-range operations without depending on support from Germany and to move far from her supply ships to hunt Allied shipping as she pleased. Her ability to rendezvous with supply ships like Rekum and Eurofeld also helped the Thor sustain her two long cruises, which saw the ship travel throughout the Atlantic, Indian and Southern Oceans to hunt Allied shipping. Thor’s versatility was also emphasized by her ability to take on tasks other than commerce raiding; she was also capable of supporting reconnaissance and mine-laying operations, which she carried out with her seaplane and sea mines. Thor was also able to stay in service longer than most of her sister ships thanks to her ability to stay at sea for long periods without needing to resupply. The Thor’s air advantage and self-sustainability would see her further improved in her second cruise when she was refitted with radar equipment to better locate targets and avoid Allied warships.

Key Roles in Battles and Operations

First Cruise: Atlantic and Indian Oceans (June 1940–April 1941)

Thor began its first combat cruise on 6 June 1940 under the command of Kapitän zur See Otto Kähler. Thor left Kiel on 6 June 1940 and navigated into the Atlantic Ocean via the Denmark Strait, disguised as a neutral ship. Thor roamed the Atlantic, hunting and sinking Allied merchant shipping. On 1 July 1940, Thor spotted and stopped the 9,290-ton Dutch cargo ship Kertosono, which was carrying petrol, timber, asphalt and agricultural machinery. Kertosono was captured and sent to France as a prize ship with a German crew. The Thor sank the 4,231-ton Belgian freighter Bruges on 7 July 1940 and the 7,262-ton British freighter Gracefield on 9 July 1940, both by gunfire after capturing the crew. On 14 July 1940, the Thor encountered the 22,209-ton British armed merchant cruiser HMS Alcantara. Alcantara was a large and heavily armed merchant cruiser, with a battery of eight 6-inch guns. Kähler used a stern chase to bring Thor’s broadside to bear on Alcantara, landing eight hits in the process. Alcantara broke off contact to return to Rio de Janeiro, Brazil for repairs. Thor’s guns suffered from overheating but were later repaired at sea.

Thor rendezvoused with supply ship Rekum on 25 August 1940 and after repairs, it returned to Brazilian waters. On 8 September 1940, Thor stopped the neutral Yugoslav Federico Glavic but allowed it to leave. On 26 September 1940, the Thor’s seaplane spotted the 10,730-ton Norwegian whale-oil tanker Kosmos, which was carrying 17,000 tons of whale oil. Kähler determined that Kosmos was too slow and too easily identifiable as a prize for her to capture Kosmos for a prize ship, and so the Thor sank the Kosmos by gunfire. On 8 October 1940, the Thor sank the 8,715-ton British reefer Natia with a single direct hit to the engine room. Kähler was able to track Natia’s position on its wireless transmissions while the ship was sinking. On 5 December 1940, Thor encountered the 20,062-ton British armed merchant cruiser HMS Carnarvon Castle. Carnarvon Castle was a large and well-armed merchant cruiser, armed with a battery of eight 6-inch guns. Kähler used a stern chase to engage the Carnarvon Castle in a head-to-head fight and landed over 20 hits. Carnarvon Castle disengaged and returned to Montevideo, Uruguay for repairs. Six of her crew were killed and 32 wounded. Thor’s guns jammed from overheating and had to be repaired at sea. The British battleship HMS Rodney, the aircraft carrier HMS Ark Royal, the light cruisers HMS Enterprise and HMS Cumberland, and the destroyers HMS Newcastle, Nestor and Foresight searched for the Thor with no success.

Thor resupplied on 21 December 1940 from supply ship Eurofeld. Thor later met up with the Admiral Scheer on 25 December 1940 to transfer crew to the raider’s prize ships after it was captured by the raider Pinguin. In March 1941, the Thor sank the 7,504-ton British ships Britannia and Trolleholm and captured the 9,276-ton Swedish ore carrier Trolleholm and the 10,490-ton Panamanian tanker Heraklia. The Thor returned to Hamburg on 30 April 1941 after 329 days at sea, with 12 ships sunk or captured with a total of 96,547 gross register tons.

Atlantic and Southern Oceans (November 1941–October 1942)

The Thor had a close-quarters collision with the Swedish ore carrier Bothnia in thick fog while sailing south of Cape Horn. The Thor had to return to Kiel for the fitting of a new bow. The Thor was refitted with a newer set of guns and was also given newer radar equipment for the new cruise. Thor began her second combat cruise on 30 November 1941 under Kapitän zur See Günther Gumprich. Thor sailed close to the French coast and through the Bay of Biscay before heading out into the Atlantic Ocean on 14 January 1942, delayed by several storms. Thor then started south towards the Antarctic to provide relief to Kormoran in the Indian Ocean, but was ordered to the Southern Ocean instead. The Thor crossed the Antarctic Circle on 25 February 1942 and searched for whaling fleets with her Arado seaplane. Thor found no whaling fleets but managed to pick up shortwave transmissions.

On 23 March 1942, the Thor sank the 7,374-ton Greek freighter Pagasitikos, the 8,530-ton British freighter Wellpark on 30 March 1942, the 5,637-ton Norwegian freighter Aust on 31 March 1942 and the 6,146-ton British steamer Kirkpool on 2 April 1942. In June 1942, Thor operated off South Africa, and it sank the 8,764-ton British ships Olivia and Gloucester Castle on 1 June 1942 and 15 June 1942 respectively. On 4 July 1942, Thor sank the 6,681-ton Norwegian ship Madrono and the 7,012-ton British tanker Indus on 20 July 1942. The Thor’s second cruise was marked by the Thor’s radar advantage over Allied ships in the area, allowing her to avoid Allied warships and engage with targets of her choosing. Thor also rendezvoused with the supply ship Regensburg to transfer prisoners captured from the ships she sunk and to resupply from Regensburg. On 9 October 1942, the Thor was sunk by an accidental fire aboard supply ship Uckermark in Yokohama, Japan while the Thor was refueling, ending her second cruise with 10 ships sunk or captured, with a total of 56,037 tons.

Final thoughts

Thor’s two combat cruises resulted in 22 ships sunk or captured with a total of over 150,000 gross register tons, one of the more successful tally among the nine German merchant raiders. Thor’s battles with HMS Alcantara and HMS Carnarvon Castle demonstrated its ability to take on armed merchant cruisers with a comparable armament, but also highlighted its tactical advantages such as superior disguise and deception tactics. Thor also saw combat in many other important commerce-raiding operations as she roamed the Atlantic and Indian Oceans on her first cruise and the Southern Ocean on her second, as the commerce raider harassed Allied shipping in an attempt to disrupt their supply lines. Thor’s impact on Allied shipping was effective as her commerce-raiding success forced the Allies to divert significant naval and air resources to hunt for her. Thor’s use of radar on her second cruise marked a turning point in the evolution of commerce raiding for the Kriegsmarine, but its loss in an accidental fire marked the vulnerability of its commerce raiders once they operated too far from German ports and support.

Thor’s legacy was in its important part in Germany’s commerce-raiding strategy, which put a strain on Allied logistics and shipping operations at a critical juncture of the war. Thor’s operation across three oceans, from the Atlantic to the Antarctic, also demonstrated the Kriegsmarine’s global reach and ingenuity in deploying auxiliary cruisers in efforts to neutralize the Allies’ advantage at sea. Thor’s operational history was a microcosm of Germany’s larger challenges in its naval campaign against the Allies, as it was also able to achieve many notable tactical successes while also being unable to make any long-term impact on the Allies’ larger resource advantage.